Keeps coming loose,can I change it to 6 bolts or am I for some new wheels?

Could try some kind of locktite product on the bolts or a different adaptor? Never used an adaptor myself but those would be my first things to try. Failing that new rotors?

Edit…have you got centre lock hubs and 6 bolt rotors? Either way new rotors would be cheaper than new wheels or am I totally missing something!?

No not for centre lock rotors,same sort of principle,the rotor bolts are just pins that are mounted to the hub then a centre lock style system that you tighten with a hollowtech bob tool.
The pins that hold the rotors in place are 1mm to small so the play when braking causes the rotors to work loose,I would just like to change them so I can just bolt it on.