Legal Question in Family Law in Washington

You need to file and serve a Notice of Intent to Relocate (likely referenced in your Parenting Plan) and serve it with 60 days' notice, although there are some exceptions if you cannot provide 60 days' notice. You also need a new proposed Parenting Plan, and then the other side has an opportunity to contest the relocation, otherwise, your proposed plan will be come the new Parenting Plan.

I suggest you seek legal counsel to help you with this, since the last thing you want is an error or defect in the way you handled things, that results in trouble that could otherwise have been avoided.