modifications do i have to do? my engine is toast so i fugured i would put a bigger engine in it.

You are talking front wheel drive and rear . It would be cheaper to buy a Supra.

well, the 95 celica is a front wheel drive, where as the supra is a rear wheel drive, so
you would have to
- cut apart the firewall and center line of the car to fit the transmission and driveshaft
- custom make a way to hold the rear differential in place
- somehow fit the huge motor into the tiny bay
- rewire the engine into the cars stock wiring harness, so everything would read correctly at the gauges, and so the ecu would work properly
- and make custom motor/trans mounts, a custom driveshaft, and custom axles.