If it's the same both sides I wouldn't worry about it too much. But from the photo, the nut slots are all different heights. Normally you could just remove the nut, sand the bottom down a bit and replace it to get the strings lower. But with such unevenness, I'd be looking at cutting the slots deeper, and then filing down the top of the nut a bit (though that bit is optional). But to cut the slots properly, you really need a set of nut files, and good ones aren't cheap. For a once- or twice-off job, it's cheaper taking it to a luthier to do, but once you get to 3+ guitars, it's probably time to invest in some nut files.

Alternatively there may be some PBG forum members in the Perth area who could do it for you.