tyres

Greetings y'all! I am a complete noob when it comes to knowledge about tires. I'm currently running on the stock set of Firestones that the 2015 S+ comes with and am coming up on 40k miles, 5k mine and 35k the previous owners. I have begun to notice why people on this forum give the stock tires...

what size rims and tyres can i go up to, ive got a 1993 corolla seca liftback and i want to put some fat tyres on it, any suggestions?