With Disk Cleanup you can "transform" your hard drive by removing a lot of the unwanted, unnecessary junk that can accumulate and clutter your system.

To access Disk Cleanup, first click on the Start Menu, then click Computer. Right-click on your C: drive, click on Properties and then click Disk Cleanup.

This will scan the system and find all of the files that can be deleted to free up more space on your hard drive.

Choose which files you would like to delete by checking the box next to the item(s) and clicking OK. In the video, System error memory dump files is unnecessary. 

After you click OK, click Delete Files in the dialogue box that pops up.

After you've deleted the files, you'll want to check the drive for errors. To do this, open the Tools tab in the Properties box and click Check now…

In the Check Disk box that pops up, make sure Scan for and attempt recovery of bad sectors is checked (along with Automatically fix file system errors) before you click Start.

You might not be able to check the disk at the moment if it's the same drive you're using to run your operating system, so you may be asked to Schedule disk check. This will run a check on the drive the next time you start your computer, before Windows loads.