The heat gun or hair dryer to remove the lettering. Any goo remover (just read the label first) would
work, or mineral spirits, or diluted acetone. Mineral spirits take a few passes to remove softened goo but are safe on
gelcoat, acetone is faster but reacts with
gelcoat so be measured and quick.
Do not use anything sharp nor abrasive unless you are planning to do gelcoat compounding, which you might need to do anyway ... the gelcoat under the existing lettering will be shiny new.