Installing disc brakes is more often than not, a considerable upgrade for anyone who is serious about their mountain biking. You won’t have to worry about wearing down your rims and about trying to break when it’s wet outside.
That said, back in the day, it would have been real difficult to adapt a v-brake bike into a disc brake because disc brake manufacturers did not make them to be compatible with other systems until the introduction of the Six-Bolt International Standard (I.S. for short) in the mid 1990s. So if your wheels are older than that, buyer beware.
I’ve scoured for a decent video for this tutorial and this really was the only one that went into it at depth. The problem I have with it is that the mechanic should have been using gloves when installing the rotors. Fingers secrete oils and if they get into the brake pads, they will reduce in efficiency. And if you brake and contaminate the brake pads with the oil from your hands, you may be off to the store buying new ones. If you do end up touching the discs, wipe them down with solvent and then, with a dry corner of a rag, wipe it down again.
The video is for Avid hydraulic brake installation.
Affix your rotors to your wheels, remove the v-brakes, mount the hydraulic caliper brakes and measure out your housing.
And use gloves when handling the rotors. Better safe than sorry.