Replacing electrical wiring
This is not an answer, but it's too long for a comment:

Consider the cost. A 4x8 sheet of Sheetrock ~$11. A contractor who has an electrical license is $75-150 per hour in my area. 
If you can find one who needs work. 
Some use small jobs as fillers but I find that a small job of updating a room can turn into a can of worms and take all day so it will usually be quoted T &amp; M (Time and materials).

I find it easier to replace a panel than update old wiring, and the panel pays better, no crawling, + usually decent work area. (I don’t go under most houses - that is for the apprentices.) 

Just trying to give you an idea of what to expect. Electricians are in short supply in the Pacific Northwest, and if the job is a PITA you might have trouble getting it done. Without opening the walls the job may cost 5×, but open the walls and the PITA factor drops and the price also along with the unknown factor.

You may find a hungry electrician out there but use caution &amp; have a contract! Understand sometimes the cheapest quote up front may be the most expensive in the long run. Try to find someone with references, not just online stars. 

And since this is a DIY site it may be a chance for you to learn and  save a few bucks. Going from a 15 to 20 amp circuit is quite simple: you are just installing #12 wiring. Take photos of each connection prior to taking it apart.  Mark wires with numbers if you think you will get things mixed up. After upgrading the wire size on the circuit snap in a 20 amp breaker and you have done it.

(In my state repair of a circuit - in this case just replacing individual components - doesn’t require a permit and can be done by a homeowner. Check your local regulations as from what I have read some states require an electrician for simple “device” outlet or switch  changes).