Security Deposit Money To Cover Repairs?

I have a rental that's been rented out for about 4 years to the same tenants. At this point they are month-to-month and I only need 30-day notice to ask them to move. I'm planning to ask them to move out soon because I'm planning to sell the property.

My question is - what am I allowed to use their security deposit for exactly? Does it make any difference if they have been living in the house for 1 year or 4 years when it comes to what I'm allowed to use the money for?