HI ,
There is no simplified ways to convert a SPOT VM to regular VM of a Regular VM to a SPOT VM , this can be achieved using CLI but may require Downtime and sometimes may result in failure.
You need to take Snapshot for the OS Disk , then Delete the VM without deleting the IP and Disk attached.
Once Done , you can recreate a Regular VM with the Snapshot of the OS Disk and attach the Disks and IP that was preserved from the earlier activity.