Replace v-brakes with disc brakes I would like to know whether I can replace my old v-brakes with disc brakes. Do I need to also change the wheels or something else?
You need to have the appropriate mounts on the fork, the rear of the frame, and you need hubs that can accept disc rotors.
My understanding is that some older MTB frames and forks had mounts for both V- and disc brakes. This was when the industry was starting to shift towards disc brakes. While I'm not familiar with MTBs, that might have been in the early 2000s. If you don't have the correct frame mounts, then there's obviously no way to proceed at all.
Even if you do have disc mounts on the frame and fork, I suspect your hubs were rim brake only, so it would be quite a costly upgrade. It's likely more economical to sell the bike or repurpose it as a commuter.