Right now the only ways to level up a character are reading books, learning through real-life experience (which gains bonuses with higher focus), and learning from NPC’s (which can be very buggy at times).
Stats can currently only be raised through traits/bionics (though I’m currently working on balancing a system that lets you gain some stat boosts through work) and resistance can only be raised through traits/bionics. (Small other note, currently HP is bugged in that it doesn’t go up when STR does, this is a bug that should eventually be addressed.)