Ladders, making the character climb up and down

Hey,

I'm creating this game where you need to climb invisible ladders to get the next room(s). The wall texture already has the ladder on it. I've been reading that I could create a trigger around the area and make w & s go up instead of forward/back or setting gravity to 0 and lowering speed? I was wondering how I could do that within the trigger script and which method is the best way?

I would need help with the Torquescript code. Please help, thank you very much!!