Systems change with the time

I'm currently running a game of Pathfinder taking place in the typical medieval fantasy settling. At the end of this campaign I'm wanting to continue the world, but jump ahead to another technological era. I'm now faced with trying to decide what I should do as far as game systems go. I want to keep the races that exist in my world and even most of the classes if I can, but I want to make sure my rules support the regular use of modern and futuristic firearms and vehicles such as cars and eventually space ships. Does anyone else who has done this have an pointers, as to whether they used new rules within their original system to support the change in technology, or did they use a new system and alter the old races and classes to work? Thank you!

Starfinder is Pathfinder with a sci-fi twist. Might be what you want without making a whole new system from scratch.

Yeah, just grab Starfinder. No need to change ruleset too much (it's not identlical, but it's 90% compatible).