How do you remove a master cylinder on a 1989 celica?

While I would suggest getting a Haynes manual, which will walk you through the whole job with pictures and details, I will say that a master cylinder is fairly easy to remove and replace. Only two bolts typically hold it to the power brake booster, which is located on the firewall. You will need flare nut wrenches to loosen all of the brake line connections at the master cylinder. Then loosen the bolts that hold the MC to the power brake booster -- usually one on either side of the MC. Remove, bench bleed the new MC, and replace it.

Bleed your brakes 1st. You might not even have to replace the Master Cylinder.