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Windows needs a certain amount of free space on your drive to perform well. If your drive is too full, your computer may slow to a crawl or you might experience errors. Microsoft doesn't specify exactly how much free space you should have, but the general rule of thumb is about 20% of your hard disk capacity, or 2.5X the amount of RAM you have installed.  You can check how large your hard disk is by pressing ⊞ Win+E and selecting your hard drive. It is more important to keep free space on your Windows hard disk if you have more than one installed. You can check how much RAM you have installed by pressing ⊞ Win+Pause. ⊞ Win+R and type cleanmgr. This will launch the Disk Cleanup utility. This utility will scan your hard drive and remove unused and old temporary files. You can free up a significant amount of space using this utility. This is typically the C: drive. Disk Cleanup will scan the drive for files to be removed, which may take a few minutes. The amount of space you will recover will be listed next to each entry. Generally, it is safe to remove everything that Disk Cleanup reports. Clean up system files button. Once you have everything checked, click the button to remove the files. Disk Cleanup will handle the process automatically.

Summary:
Delete old files that you don't use anymore. Press . Select your hard disk. Check the box for each item you want to remove. Click the .