Is it a natural transition to go from sitting down to standing up? IMO, not so much.

Granted, over the years these musicians and others vary the way they hold the instrument and sometimes I think it's more to do with fashion (what looks good or cool). Still the important thing is to hold the guitar in a way that allows for fretboard access, proper position of the fret hand and ease and comfort of playing. After that, it's up to you.

Good luck, have fun.

john

Oh yeah... the size of the guitar and one's own body size and shape comes into play too