It might be slightly different for other operating systems though.
Before we begin with the steps, here are some important notes you might want to consider:
1. Your files and folders will not be deleted or harmed in any way.
2. You are advised to keep your power plugged in when following these steps if you’re using a laptop.
3. It’s highly recommended that you do all of this every couple of months to maintain the speed, performance and memory of your computer.

Step 1: Empty Your Recycle Bin

Many people have more than 3000+ files in their recycle bin! Keeping these files takes up a lot of space in your computer’s memory and it might also affect the speed of your RAM memory (random access memory, is the memory that is used for short times while running any software on your computer).
Always empty your recycle bin! Just look at the icon on your desktop, if the bin was full, simply right-click and choose empty recycle bin.

Step 2: Uninstall Unwanted Or Trial Programs & Software

Sometimes people like to install games or programs that are only trials (trials usually take 30 days). When the trial expires, the game or program are still on your computer even though you’re no longer using it! This can also take up a lot of your computer’s space. To uninstall a program or software, simply go to Control Panel >> Add or remove programs and then just uninstall the programs that you’re not using. If there’s a software that you have not installed yourself, keep it on your system because it usually has something to do with your computer’s hardware devices. For example, if you find a software that looks something like: “WIDCOMM Bluetooth Software”, then you will know that it’s something that deals with your computer’s bluetooth device. If you delete a software like this by accident, you will have to visit your computer’s manufacturing website, they usually offer these software programs free to download, you might need to know your computer’s model or name so that you make sure you’re downloading the right programs.

Step 3: Clean Up Your Memory

When your computer executes your instructions, it uses the memory to save “temporary” files which it will use while it’s working. This means that even though your recycle bin is empty, there are still other unnecessary files all over your computer. To delete those files simply go to Start >> All programs >> Accessories >> System tools >> Disk cleanup.

Something like this will show up, choose the disk you want to clean and click OK. (Note that your files and folders will not be deleted or harmed in any way!) I recommend cleaning all of your disks, one after the other!

Just wait a little while until it calculates all your files and folders (This might take some time if you’ve never done it before!).

Now when this shows up, just make sure there’s a little green “check” sign is next to everything, if it’s not, simply check them all. Now click OK and then click Yes! Again, don’t worry about your files, they won’t be deleted!!

Step 4: Check Your System For Errors

Sometimes viruses and computer errors can cause your computer to slow down… In this case, you need to check your system for errors.

Go to My computer >> Then right-click on your drive C >> choose Properties.

Choose Tools >> Check now.

Make sure that both items are checked!! And then click Start. Sometimes, it requires you to restart your computer and when it’s restarting a black and white screen will appear, just don’t click anything until it’s done checking your system for errors!

Now if you suspect that you have a virus on your computer, then having an anti-virus software could come in hand. Most computers come with an anti-virus software, but if you don’t have one, simply use Symantec.Com to get one for your computer.

Step 5: Disk Defragmenter

When you save an image or a file on your computer, the system saves them in the first available space on your memory, causing many unrelated files to squeeze in together! This “disk fragmentation” causes your system to slow down dramatically, and you need to de-fragment your disk!
To do that, go to Start >> All programs >> Accessories >> System tools >> Disk Defragmenter.

Just choose the disk you want to defragment and click Defragment… Again, I recommend repeating this to all your disks!

And There You Have It

After doing all of the above, your computer should be looking pretty good in it’s speed and performance. It should also empty some of your memory, which is always a good thing to have. If for some reason your computer was still very slow, you might need to format your entire PC, but these 5 steps usually give great results for your computer.