Can I convert the brakes from rim to disc I have a 1990s vertik 2 it's the mountain bike one and I am wondering if I could convert the rim brakes to disc brakes if so what are good budget options
No.

You would require new wheel hubs with a disk rotor mount, and you would need a fork and a frame with caliper mounts.

Once you replace the fork, frame, and wheel hubs, its not economical.

Instead, shout yourself to some new rim brake pads.  Good kool-stop ones will improve your braking and it feels like a decent upgrade, for much cheaper.