I've done mine twice now. I made myself a level ramp 40 cm high out of laid breeze blocks specially for working on gearboxes!
The job is fairly easy BUT the gearbox is very heavy. My estimate is 80 or 90Kg. You need two preferably strong people and one or two good trolley jacks. It isn't a job to rush at as you can injure yourself if the car isn't safely supported or the gearbox safely handled.
The mechanics are undoing electrical conectors, prop shaf end connection, gearbox mounts, bell house bolts. On a four pot, I suspect you don't have to take the exhaust off unlike on the V6's.
The key piece of advice is to take it off the engine level and put the replacement on level i.e. not let the bellhouse end hang off the spigot. You also need to ensure that it is mated up properly. That is covered on here maybe in the maintenance guides I believe.
Has yours had it? presumably you have done the usual things like oil and filter change, looked for any faults causing it to safe mode and set off in third gear or issues with solenoids?