An unlawful detainer lawsuit is the court action that allows California landlords to evict and remove tenants who refuse to leave. The process for evicting relatives is the same as for evicting any other tenant, unless the tenant is a minor child, your spouse or shares ownership of the property. Out of respect for your relative, it's a good idea to give him more notice than is required by law and to avoid taking him to court if possible. Otherwise, you must follow the legal process for evicting someone and can't simply remove your relative's items from the property or change the locks.
Give your relative notice that you want him to leave the property. If he's failed to pay rent, you must give him three days' notice. He then has three days to pay rent or be evicted. If you want to terminate the tenancy for any other reason, you must give him 30 days' notice if he's lived in the property for less than a year and 60 days if he's lived there more than a year. If you have a lease with your relative, you must follow the provisions of the lease, unless the lease specifies less time than the law. The notice should be in writing and sent via certified mail, with return-receipt requested.
File an eviction suit with the magistrate court clerk in the county where the property is. Fill out the forms the clerk gives you and attach copies of the notice you sent to your relative. The eviction hearing will usually be scheduled within 10 days from the date of filing. You should not remove your relative's possessions from the property or change the locks prior to the eviction hearing.
Attend the eviction hearing. Your relative will have the chance to plead his case and fight the eviction, so you should be prepared with your evidence. If you win the eviction hearing, the judge will give your relative a writ of possession, which requires him to leave within five days. If he won't leave at the end of the five-day period, the sheriff will remove his possessions from the property and you'll be allowed to change the locks.
If the relative is not a tenant and is instead a guest who has overstayed her welcome, simply ask her to leave. If she won't leave, it's considered trespassing and you have the right to call the police.
Some municipalities in California require that a landlord show "just cause" for evicting a tenant and can't simply terminate a tenancy. If you live in a rent-controlled area, contact your local municipal court for more information.