How to make different StarterPlayers?

So, me and a friend are working on a game that is a minigame-per-minigame Roblox game. The game is about Blocky-like creatures called "Blocketts" (image: http://prntscr.com/j954qw) who Fight on a tournament of 25 Minigames to see who gets more points (You get more depending of position), Each minigame beated gives you Clay Coins, Something you can use on a machine to turn yourself into other blocketts, which have different WalkSpeed, JumpPower and Health, Plus, using the clay coins let's you Buy snacks to level up, Leveling up lets you boost any of the already mentioned stats per 1 point, Plus after reaching a certain level, you get extra skills to either attack players, Help them, or only for your advantage, And after a tournament ends, The player with more points wins, getting more clay coins, And the others get compensation prizes depending on their positions.

Ok, i literally gave us potential to steal my idea, however, the thing is:

As i said, Players can turn into Blocketts, I already have the models, And i know how to use StarterCharacter, I tested it on a character, and it works perfectly.

I need to make that you can change the startercharacter (aka: playermodel). Just as simplified version is that, when touching a part, the normal robloxian charactermodel gets changed to a blockett model.

Link of the model: https://web.roblox.com/catalog/1660083275/redirect

Thanks for reading that wall of text that i wrote up there, and i wish us could lend me a hand.