Did you work out how to add line-breaks now?
Choose the 'Special' tab under Stats, and double-click to add Newline, then use the up/down arrows in the middle to put it where you want.
If you want to remove some stats, double-click them in the list on the right.
If you want to revert to the default layout, stop PT3 and rename the file:
c:\program files\pokertracker 3\data\layouts.pt3
..to layouts.old and PT3 will recreate the default when you start again.
Have a look at the
How To: Advanced HUD Configuration.