Altering a mens dress shirt

Hello All~

I was just curious - I have quite a few dress shirts that are a tad too
big on me - but I still like the shirts. I was just curious as to how
easy it would be to alter them into a size that fits me better - i.e.
altering one from a 16 down to a 15 - I'm mainly just concerned with
the seams on the sides - the sleeves and collar would stay the same

Think of me a someone who's hardly used a sewing machine ;o)
thanks in advance
Mike