When you save your returns, you can use File>Save As to s...

[hoser1234]

So in other words, the answer to the question posed is you CANNOT change the default file location.

There are of course ways to do a save-as or a file move, but none of those approaches changes the default file location as requested.  TurboTax will create a TurboTax sub-directory under the logged-in user ID every time TutboTax is launched, and unless steps are taken to override the location (i.e., doing a save-as), will save to its default location.