What is the difference between douyatte and douyattara?
As in the other answer, it can be the same in some cases. However, they may have the different nuance. My analysis is the following:
If you say どうやって大阪に行けますか？ at the tourist agency. You might be asking what kind of choice I have for going to Osaka? By overnight bus? By train? By ship? It's simply asking about choices.
If you say どうやったら大阪に行けますか? at the tourist agency, It can be semantically the same. You are asking the choices. However this time, you are more of saying you do want to go to Osaka in addition to simply asking choices.