I took my old ones off using a heat gun and peeling them by hand. I buffed and polished the boat after that. I used acetone to prep the surface. If you are afraid of acetone, just use some rubbing alcohol. I measured and used masking tape to get the alignment right. It's tough to figure out exactly where you want them and what you want to reference to.
A lot of people spray a soapy water mix then apply the decals and squeeze the water out from behind the decals. I didn't do this, but I wish I had. I ended up with a few air bubbles in mine. They are really tough to get out after the fact with the drip molded decals. 99% of people could look closely at the decals and never notice the air bubbles, but they kinda bother me.
This video shows the method I was trying to describe. Where is that guy from? I've never heard anyone pronounce decal like that.