Use Level Boost Tickets that you get as tour rewards or purchases from the shop.
Everything in Mario Kart Tour has a level associated with it. Whether that’s your character, kart, or glider, everything can be leveled up. Leveling up your characters allows you to earn different bonuses and rewards in-race which will make you a better overall player. There are some different ways to level your characters in Mario Kart Tour but your primary method of doing so will be done through level-boost tickets.
So where do you get these tickets and how do you apply them? Let’s start with what are the level boost tickets and where do you get them. The best way to get Level Boost tickets is through playing the game and earning Tour Rewards as Level Boost tickets are one of the rewards in this pool. (Gold Pass subscribers will get more tour gifts than non subs so you’ll definitely get more level boosts as a paying player). However, you can still get them when playing for free, it’ll just take more time.
Level boost tickets can also show up in the shop. So check back as the inventory rotates with new items. Not all boost tickets are the same though. Make sure you’re purchasing level boost tickets for the characters and not for the glider or kart. Each has it’s own specific type of level boost tickets. The one you’re looking for to level up characters is the one with Mario’s head on it.
Once you’ve got a level ticket you can simply head into the character menu under “Drivers”, select which driver you want to level-up and then click on the Skill Box. This will open up the level-up screen where you can apply any tickets that you’ve earned from Tour Rewards or purchases.
More on Attack of the Fanboy :
Attack of the Fanboy / GAME GUIDES / Mario Kart Tour – How to Level Up Characters