No wonder people are confused with all the possible options. As you alleady have a licence, then its far easier to renew that, than mess about gaining other licences. To renew the licence you will need a valid Class rating, this has to be done at an ATO. A few hours training followed by a "Proficiency Check" (No such thing as a mini skills test!) You could do that in either a TMG or an SEP, or both, once you have both valid, you can keep both classes valid by flying just one or both classes. As already stated there are only a few schools that can train for the TMG.