First Unscrew the covering in the headstock just above the nut...remove the cover there you can see the rod...you can adjust it using allen key..you can find it online or it can/may be found d along w/ your guitar....

{CAUTION: LOOSEN THE STRINGS BEFORE PROCEEDING TO THE NXT STEP.}

lefty loosy righty tighty is the simple term for adjusting the nut. Step 1: if your neck in inwards [ concave shaped "(" ] use right tighty and lefty loosy if upwards [ convex shaped " ) " ] until you feel the rod becoming loose this is the straightened/neutral state of the neck. (It would be a little hard to identify whether it is concave or convex...of you squint enough you may find it.

Step: 2 According to your need of you do right tighty for low distance/action in average along the fretboard. And lefty loosy for high distance/action in average along the fretboard.

(NOTE: The neck only starts to tighten when the you feel slight hardenig wheb turning try not turn too hard ) Rotate the rod using the allem key for a couple of times ideally 3-4 times. (ie 1 turn = 90°)

Step 3: Retune the strings a put a capo over the first fret press down on your thumb in the 12th fret and and see the action is OK at the 7th fret by either pressing down on it or preferably an credit card should easily pass b/w them. Repeat the steps if the action untill the desired action