Re: How do I remove an up bow from a neck?
as someone mentioned, and it is a single rod (no idea what they use in a squire but I assume)... and it's not fixable via adding a washer... or the wood is collapsed... not fixable by just changing to lighter strings... You could probably buy a good quality neck on evilbay for $150 or less.
since it's a squire I doubt you are going to want to pay what a luthier would charge for this. You might take it to one for an evaluation tho... let him tell you what he thinks the problem is - might use that.
if it's that bad - the right way to fix it is to steam off the fretboard, sand flat, remove all glue, re-glue it. It's darn near as much work as building a neck IMO. Could look around for luthier schools near you and see if a student would take it on as a project... but you may not like it when you get it back.
you could use it as an opportunity to learn a bunch of things(this option gets my vote). remove frets, get appropriate radius sanding block, setup it up with the same bow once you have the strings off... sand it flat... maybe even sand in a little back bow. there is a good chance this would fix it permanently but no guarantee as when you sand wood its moisture is going to change in the sanded area... and it's going to change over a few days. You could anticipate that, let it sit, and hit it again with the radius block. If you did that I think your chances would go up to 70% or more. At the end of that if it isn't right you are only out the price of a sanding block, and new frets.
I had a 90's carvin that had similar bow issues(wish I knew now what I didn't know then). I had a well respected california luthier try to fix it and he gave it back to me without charge as nothing he tried worked. I live in AZ and had done a number of things to try and fix it with heat. I actually fixed it several times... but after a while it would return. out of frustration I even clamped it to a straight piece of aluminum and left it in my garage in 115degrees for a week. It fixed it again... week later it was back to normal. It still played pretty good but I like very low action and out of disgust I basically traded it for magic beans a few years back.
the way you prevent this type of issue, is to look down the neck when you are buying. if it's a little bow - that's one thing... if it's a lot - pass.
Here's wishing this turns out really well for you!