Is there a way to enlarge the armholes of a knit top?

Close-fitted sleeves won’t do for someone with flabby old arms. Even in larger sizes, tops don’t seem to allow much room in that area.

I used to have considerable skill in sewing, including with improvisation, but I haven’t used my machine in years. Still, I could manage if someone showed me what to do.

I’m thinking that if I turn long sleeves into ¾ sleeves and re-hem them, I can use the extra material to open up the garment around the upper arm. I just can’t quite picture the pattern or the order of operations.

How would I do this?

I’m looking at a top I really like. Should I buy two and take one apart? That seems so savage.