So I finally got my sc registration numbers, now time to put them on the boat. So what’s the best way to take off the old numbers? I have a tracker 175 pro team. All input is welcome…thanks 

Peel off best you can - plastic putty knife and Goo Gone...clean up with alcohol

 

That's how I took off the numbers, State sticker and original Alumacraft Decal from the Bass Trek anyway.

What @MN Fisher said also use a heat gun or a blow dryer first to soften the adhesive.

And some adhesives can easily be removed with WD40. Great for cleaning up the left over adhesive. Just be sure to wash the area well to remove the WD, or the new numbers will not stay stuck on the boat for long. (Don't ask how I know this.)

 

Check a small area with acetone.  If it doesn’t damage the paint, it will get things squeaky clean.

All the mentioned things and some scotch !!  No matter it is a real pain to remove them !!

3 minutes ago, airshot said:

and some scotch

Ummm - nope

 

Heat gun first to warm it and then pull it off as whole as possible.  Often it's own glue is the best at removing stuck on glue.  Goo gone works, but you can also buy 3m (or generic) pinstripe removal erasers that pop in your drill.

Naphtha.  It's safe on most finishes and plastics and will dissolve adhesives very quickly.  Just pour a little on, let it soak for about 30 seconds, then work the sticker off, starting from a corner.  If it's still sticky, pour a little more on under the sticker and let it work its way through.  

 

It's much safer than most other solvents like acetone or mineral spirits, while still being effective.  Plus, it's readily available just about everywhere, either a hardware store as naphtha or a convenience/grocery/general store, sold under the brand name Ronsonol (cigarette lighter fluid, not charcoal grill lighter fluid, which also might work, but I don't know how safe it is).  

A little elbow grease may be necessary depending on how long the old numbers have been on. Are they on the decals of the 175 or do you have just the straight aluminum version?

22 hours ago, MN Fisher said:

Ummm - nope

 

That also works !!

https://www.harborfreight.com/4-piece-nonmarring-scraper-set-95832.html