Actually there's nothing difficult. The main thing - to remove the excess. In the first place I recommend to download the program ССleaner is a good program that will independently monitor the amount of unnecessary information on the drive, fix bugs and so on. The interface is intuitive, it places occupies a little, and use the car. So the first step is run the program and delete everything unnecessary.
Step two - start the computer in safe mode.

Windows 7 is F8. When the computer is starting press F8 several times and you should see a black screen where you arrows to choose "Start in safe mode". If F8 does not work, press the Fn key, it will include a panel with function keys. Maybe not the first time (I did it 4-5 times), you still enter in safe mode.

For Windows 8, simultaneously press the key with the Windows icon, and R. In the window that appears, enter msconfig and click OK. In the tab "Loading" put a check on safe mode and restart your computer.
The list of folders that can be cleaned without fear delete something you need.

%username% - user name
Press CTRL+A (or CTRL+f for the Russian layout) and highlight all the files. Press SHIFT+DEL and all files are deleted directly without moving to trash. By the way, the basket after all the deletions is clean. Restart your computer.