The help section is up to date & the answer is in the Help section of the all the Kano Apps.
Each time you level up you will receive bonus stamina up to a maximum of 50 or your characters max whichever is less.
You get a refill of 50 stamina. If you have qty 5 stam when you level you are refilled 50 totaling 55. If you have a max of 80 stam & you have 60 when you level, it will only refill 20 to your max of 80. The same is for health & energy.