You can increase your player level by ranking up your bikes!
To rank up your bikes you must collect all of the bikes’ blueprints. You can check how many blueprints you need to upgrade each bike by going to the Duel menu and scrolling the bike options. Each bike shows in their description the amount of blueprints necessary to upgrade them.
Blueprints can be earned from Supply Crates, Ultra Crates, and Super Crates.