If 2 strokes nope, can upgrade a 4 to a 5 HP as both shares same CC powerheads. Can upgrade a 6 to an 8 or a max 9.8 HP as all 3 shares same larger CC powerheads compared to the previous mentioned models. Only need carb swaps for next higher HP models along increasing some degrees the current timing advance. More fuel intake needs slight more time advance setting, a matter to check the Service Manual for tech specs for each mentioned HP models.
Buy a 5 HP carb, install an induction tach, go for a wot spin and check if the motor runs at least towards it's middle rpm range, surely not with a factory delivered prop, if so, will need to go for a prop maximization to a less pitch for motor to run towards its max rpm range and get the max HP out of the updated 5 motor.
Happy Boating