How to change the phase from 12V to 24V

You probably need to change your control board to one that outputs 24v.

Or add a 24v power supply and modify the wiring. If it is an Atomstack 20w module, they should be able to provide everything you need (cables and instructions) for making the upgrade.

Just change the power supply and the laser module. All mainboards I ever came across can be used with either 12V and 24V without any issue.
If you have an air assist that is connected to the mainboard directly, this needs to be changed as well, but I think Atomstack didn’t have this in the early models.