Hi,
I have an 1100AH board in production running firmware 5.22 with firmware 2.39.
Is it safe to upgrade directly to 6.13?
Thanks!
No one have seen 6.13. No one knows.
upgrade first to 5.26, then upgrade firmware on board.
After that you can go to 6.xx and upgrade firmware once more
I meant 6.12 of course! 
I received an email reply from Mikrotik Support stating that it was fine to upgrade directly, which I did. No problems.