You would need to carefully check all your onboard electronics can handle the higher voltage from the 5S and your rig can handle the extra all up weight. It will also change the performance of the motor/prop combo as the motors will spin faster at a higher voltage (assuming they can handle the higher voltage) so may well have to tinker with the prop sizes to get it back where it is happy or maybe even swap out the motors for a different KV value. It might be much easier to go to a higher capacity 4S battery, i believe Desire Power make a 6200 pack or if you have space on the rig and the extra weight is manageable you could run 2 packs connected in parallel, that will take some working out and trying out to see where the tipping point (capacity V extra weight is) if you run packs in parallel you have to pay special attention to keeping them fairly matched in terms of rating,age internal resistance etc.. if they go far enough out of balance they can discharge at an unequal rate and you run the risk of one discharging into the other which is not good.