You can't change the "founded by" person in the current family tree, but you can export your family tree and import it as a new tree and set a new founding person. Note that pictures are not exported.
The only way I know to fix this is to create a copy of your tree as follows:
You should now have a copy of your tree with the corrected "me" and you can go to the My Account screen and delete the old version and rename the new tree as desired. Again, note that pictures are not exported.