Here is how I get rid of the squirrels in my attic.

First of all, you need to know from where the squirrels coming into your attic.  Get some moth balls which are pretty cheap.  Put them everywhere in your attic.  Wait for one day to make sure that they don't come back or they usally go out during the day.  When they are not in your attic, you need to seal the hole or opening where they come in.  I used a piece of metal to seal the hole since the squirrels' teeth are very tough and they can chew through the wood.  Hope this helps.  Good luck.