Agreed that updating shouldn't disturb your current game, but if you're worried about it, this wiki page will tell you where to find your save file on mobile. Just copy the save file to somewhere else (maybe transfer to PC), and then update. If your save file is somehow deleted (which, again, shouldn't happen), you can copy the old save file back to where it was on your phone.
This is also a good thing to do every once in a while just in case you lose your phone or delete all the data by accident or something (I say, hypocritically, having never done this).
EDIT: I've never bothered to back up my mobile saves, I mean. I did once delete all my data by accident. Fortunately my mobile saves are pretty casual and I enjoy early-game best (pre-1.5, at least) so I wasn't *too* bothered.
