2zz engine swap. Please help me!

Okay, to start off I would like to say that I am a sixteen year old boy who got a celica gt 2002 for his first car. Anyway, my car has about 309,000 miles on it and no sort of engine work has been done to it. My engine has been sputtering and I smell a really sweet smell after about 10 to 15 minutes of driving. The guy at auto one said that I need to have my engine rebuilt, or swapped out. The price to rebuild is way higher than it is to get a salvage gts and get the engine out. I need to know how hard the engine swap really is.