Adjusting the truss rod: generally (and this is not universal), you turn the adjuster clockwise to tighten the truss rod and decrease the bow in the neck, and anticlockwise to loosen it and increase the bow in the neck. When loosening it, you don't need to loosen the strings. When tightening it, you can loosen the strings or push back on the headstock to decrease the bow while tightening it.
The commonest truss rod adjuster is probably a 4mm allen key. A capo is also very useful - put the capo on the first fret, then hold the strings down at the top fret and see what clearance you have to frets halfway between the two. Some people like a lot of relief, others like very little - find out what suits you, sort out a way of measuring it, then you can reproduce it on other instruments or after changing string gauges or when the weather changes and the neck shifts a bit.