[QUESTION] How to move any chord up an octave

I’ve been learning songs for a while now and I’m finally starting to try understand theory on guitar.(I’m finding it quite difficult)

I have played chords an octave higher before, for example when I play the start of Old Man by Neil Young, I play d major and then play it(d major) higher.

I guess I just don’t understand how that works out on the fretboard.

how do I figure out how to play chords in the octave I want to hear them in?

Also, when I looked it up it says there’s about four octaves on a guitar fretboard, but it just completely confuses me because I know the twelfth fret is where a full octave ends.

I really think something just hasn’t clicked in my mind and maybe your comments will help. Thank you

( I completely understand how to change the octave of a chord on a piano because it’s very linear)