Unless you really want to get into building AR/M16 uppers, just pay a local gunsmith to switch the barrel to the new upper.
Cost will be around fifty bucks.
To do one correctly and minimize/ eliminate damage I recommend a good Receiver block the includes a carrier channel filler, A GOOD vice, a 1/16" roll pin punch to remove the gas tube roll pin, A small roll pin starter punch to replace the roll pin, an 8 ounce brass hammer to minimize/eliminate hammer marks, and my now all time favorite Precision Reflex handled barrel nut wrench.
You won't need headspace gages since you'll be using the same carrier & bolt assembly and barrel.
These will be needed when you decide to add a new barrel to your old handled upper.
You will also need a set of snap ring pliers to install a new Delta Ring assembly if you go that route.
I'm no great fan of free float handguards unless you're building a Match Grade rifle and many will require a good quality strap wrench to install correctly.
This is an old pic of the goodies you will need to do complete builds and some items have been upgraded or added to my personal tool kit since this photo was taken.