How do you evict a roommate in your apartment if you and one other person are on the lease and the roommate that you want to evict is not?

First of all, you and the other person on the lease must agree that the roommate should be evicted. Then, you should sit down with the roommate and try to work out a plan for the roommate to leave. Any agreement you can work out will be far easier and cheaper than using the legal process (see below).

Next, if the roommate has agreed to pay rent, buy groceries, etc. (which means he/she is not a guest) you must give the roommate written notice to leave. 20 days' notice is what most states require, but you should check out your state's law. If the roommate still refuses to leave, then you must evict him/her in the same way a landlord evicts a tenant. See How Do You Evict a Tenant? below.

If the roommate is a guest, then you will need to file a lawsuit for ejection against the roommate. Unless you are an expert at your state's civil court procedure, you will need to hire an attorney to represent you in the lawsuit.