If your tenant is on a month to month, just issue the termination of lease the the date to vacate in accordance to your state's law.
Also, issue a cure or quit notice about the lock change if your lease states the tenant cannot change the locks or must provide the LL with a copy of the key.
Filing for eviction for solely this violation will probably not work. You have to give proper notice of the violation and the opportunity for the tenant to correct it. Anything other than nonpayment of rent is hard win in LL/tenant court.