Theres two adjusters on either light, im not sure what colour they are on the VY's, (I havent adjusted mine yet??!!) I think they are little black nobs/ or 10mm nuts, just turn it either way, and watch the light move up and down,
I think you can see them from the top of the light with the bonnet open, there is cut outs in the radiator support, to allow you to adjust them.. if not there, at the back of the light, facing upwards, maybe one in the radiator support panel, and one from behind?!
Do you have a multimeter?? you can do a few tests, on either light to see if they have the same voltage getting to them, and the same resistance in the earth circuit, it maybe could even be a dodgey relay half burnt out/corroded, try swapping the relays over from right headlight to left, in the fuse box under the bonnet.. see if the dull light changes over to the left..