In main page click on the glyph next to a battle button, select a desired class from the top by selecting an appropriate glyph, read a short story about hero and click on ‘choose’ button at the bottom of the page
Joke aside I think you overdone it, especially if you consider that you only need to click once to spend crystals on card upgrade! Even though I love that there is no more games played with wrong class after finishing a practice or upgrading a card (maybe accidental swipe, does that even happens?), feel like there was less invasive way to accomplish the same thing (allow selection on main page only and only allow switching on arrows instead of swipe).
Hero stories are really a nice touch, short but sweet, gives at least some background for ppl who like that sort of stuff. Again more descriptive hero ability would be even better.
As for graphics it looks really awesome, especially on iPad big screen, shadows are crazy good, feels like a movie. And again I hate it :). First thing I do when I enter any game is strip effects on bare minimum, because I value performance and clear picture of what is going on on the screen above all. New map is to dark now imo, preventing me to use lower brightness and is somewhat annoying, but than again maybe I just need to get use to it and you implemented it because it is better for our eyes or who knows what.
Do not to get me wrong I really like that you are trying and constantly making changes and that you listen to a community, so keep doing it!!