If he's already failed to comply with the terms of the lease you can send him a comply or vacate notice now, with the exact form of the notice depending on what he failed to comply with. You cannot legally change the locks. The best approach, if it works, is to talk or negotiate him out of the house, or have his father do it. Otherwise if he won't leave when the lease runs out (or if you haven't evicted him already for noncompliance) you'll have to go to court to evict him. If you live in Seattle you'll have to satisfy its "just cause" ordinance too, but that may not be too hard as he's been living in your home. As a landlord you have a lien on his possessions for a maximum of 2 months rent, but it needs to be exercised carefully. Best if you get some legal help with this if he won't leave voluntarily.
Distress for rent (a lien on the tenant's property) was outlawed in residential tenancies in WA in 1973. If you do that, this 19 year old will have a solid basis for a replevin action, which carries the risk of having to pay his attorney fees and costs. Don't do it.
Self-help evictions in WA are frowned upon. If you have a written contract, then you have created a tenancy and need to end it according to law.