To do a system restore in windows 7, open your start menu with the circular windows icon on the bottom left:

In the small text box, search for ‘System restore’ and open the program labelled ‘System Restore’

follow through the menu by pressing next, then you'll come to This screen.

Here you will choose the restore point you’d like to go back to, press next and finish then it will proceed to restore and restart. However be aware that Restore points over 60 days are less reliable.