Can I upgrade my device licence label from 3 to 4?
No. You can just buy level 4 for its full price.
After buying the licence then can I upgrade from 3 to 4 ?
Yes. But think twice. Is the device you want to put level 4 on it appropriate? Wouldn’t be there better device with already installed level 4? License is linked to individual device, you cannot move it in the future to another device. It is very unusual to change the level from 3 to 4 because there is much more efficient and effective way: to buy new and better device to be used as ap and spare the original device to be used as client somewhere.
Than is
Thanks