With regard to the switching/changing of bracelet/NATO. I started off as a complete noob at it as well. Many Google searches have brought me theoretical knowledge of how to do it, but of course, nothing beats practice, and more practice.
A springbar tool is the foremost tool that you will need. As many have already suggested, Bergeon makes one of the best ones out there.
Bergeon 6767-F Spring Bar Tool. For myself, I am just using a simple one that came as a free gift where I got most of my NATO straps from.
What was initially a thirty minutes endeavour is now a 30 secs breeze. The world of custom straps, NATOs in all sorts of colours and leather will await you to dress up your watch to give it a whole different feel altogether.
Sizing of metal bracelets is quite another story. You will encounter springbars flying into oblivion and that by itself is the most frustrating thing to me. Once I 'gei kiang' and tried to adjust the pin on the clasp micro-adjuster at a traffic light and the springbar is still nowhere to be found. No one should be trying that in your vehicle!
You should always lay out a microfibre cloth on a flat and clean surface and with the appropriate tools, it should be a breeze. Here's a link that should help to resize your bracelet and save you that $8!
Resizing the most common bracelets
Inspiration from Kiosai today, and thought I will join in the SKX on NATO.

Have a good Sunday everyone!