If you have access from the inside, it could be pretty easy. This is how I removed a transducer that had been in place about 16 years. Unscrew the retaining ring on the inside, and push it as far up the cable as you can. Then, I just stepped on the transducer and stood on it. My tonnage popped it right out. The caulk holding it in place wasn't up to the pressure!
Assuming you are replacing it with a new one, cut the cable off the old transducer and use the old cable as the pull cord for the new one. May take some doing to pill it all the way through because you will be pulling the connector end of the new one (wider than the cable itself.) So you may have to work it around some corners and such but it's fairly easy.
Oh yeah, it you are putting a new transducer in, remember to pull all the cable through the new retaining ring on the inside of the boat so that the ring is in proper position to screw onto the transducer itself. And do that BEFORE you start pulling the cable through the boat. Don't ask me why that is an important step.