It's actually not that difficult. I haven't done it for the multi season tag, but I did exchange an archery deer tag for modern firearm, and it's the same process. You just need to go to a license dealer Monday through Friday, between 8:00 and about 4:00. The dealer has to call the WDFW in Olympia so your current tag can be deleted from the system, and only then will the license dealer be able to sell you your new multi-season tag. Also make sure you have the tag with you, since that needs to be turned in when they issue the new tag.