First of all, you have to start with a Notice to Quit. This form is available on line or at a courthouse. After the time period expires for him vacating under the NTQ, then you file the eviction (summary process) complaint.
The statutes provide a number of different reasons why you can evict someone. The one you are liiking for is about someone who had a right of possession but now doesn't have it. Your son falls under this category.