Can a carrera valor mountain bike be converted to disk brakes?
Assuming this is your bike, the answer would be no.  You could technically add disk brakes on the front, but it would require changing the forks to ones that had attachment points for disk brakes. You would also have to change the wheels/hubs to ones that are compatible for mounting the disk.  There is no good method of adding disk brakes to the rear as this frame is aluminum and adding disk brake mounting points after the fact isn't a good idea.  

Why do you feel that you need disk brakes? V-Brakes can perform quite well if they are adjusted right and are good quality. A good set of v-brakes will work better than a cheap set of disk brakes.