Can I increase or decrease my maximum leverage?

Leverage is currently fixed and cannot be specified or adjusted.

Note: Even though you may not select how much leverage to use in your position as you would with isolated margin, you may still "choose" how much effective leverage to employ by sizing your positions appropriately. For example, if you post 1 BTC as collateral and take a long position in 2 contracts of BTC-PERP, your effective leverage is ~2x and your liquidation price will be adjusted as such.