There is no easy migration path. The VM would have to be deleted to change the billing.
Although there is no documentation i can point you to, you could retain the disk once the spot VM is deleted, and use that disk to spin up a custom PayG VM.
How to change Spot instance to Pay as you go instance
i've understood that right now, an already created instance as spot one, cannot be changed to "Pay as you go" one.
I'd like then to restore the VM spot ones into a "Pay as you go" ones.
Is there a best practice to achieve this goal?
How i can do this restore without losing my operating system?
If priority can be set on regular after creation, i beg your pardon, i was not able to find it!