How Do I Change My League

I was never asked to choose a league but i am somehow in legacy i would like for my league to be changed to default

Legacy league is where all the old characters with much more powerful gear got send a few patch builds ago. Unfortunately, there's no way to move your characters from that league. You'll have to either play them there or start a new character in default or hardcore default.

All characters in default (and most likely legacy as well) are going to get wiped on the start of open beta in a few months anyway. So either way, your characters won't be around forever.