I spotted this great tee as a gift for a friend (in this super lovely shop in Mildura), however only size XL was left and my friend is more of a medium fit. Thus, a quick alteration project to kick off my sewing for the new year...
First I cut off the sleeves and reduced the shoulder width by 1cm on each armhole (plus the new seam allowance will take in the shoulders a further cm). Note that you don't want to take any extra off at the bottom of the armhole however, as this will make it too big for the sleeve to fit back on nicely. Then trim off the underarm seam of the sleeve pieces so they open out flat. I also cut 2cm off each side of the tee and trimmed off the bottom hem.
Then I simply sewed it all back together using an overlocker (serger) - sleeves first, then underarm and side seams. Finally use a twin needle to resew the hem.
Voila! A size medium t-shirt. I do hope it fits!