The unfortunate truth is that a lot of people just assume they can purchase a house and rent it to whoever they want whenever they want. What you have to understand is that there are laws in place to protect tenants from their landlords. These laws prevent you from coming over and making someone homeless for no reason. If you are going to be a landlord, you need to make sure you follow the rules.
Changing the locks is a quick and easy way to prevent your tenant from getting back into your property, but it is also a quick way to go to jail. There will come a time during the eviction process where you are allowed to change the locks, doing it prematurely can get you in a lot of trouble.
Just because you own the property does not mean you can come and go whenever you place. You have limited opportunities to enter the house. Your job is to perform certain maintenance tasks. You cannot just come over without given prior notice. You have to have a reason, and the tenant had to know you were coming.
Last but not least, you are not allowed to cut off utilities and make the property uncomfortable for your tenant just because you want them to move out. This can get you in a lot of legal trouble.
If you have a tenant you do not want anymore, go through the proper channels of evicting them. Otherwise, you could end up in serious legal trouble.