[header] How to alter a shirt [title] Lay the well-fitting shirt over the ill-fitting shirt. [step] Lay your ill-fitting t-shirt out flat and then lay the well-fitting shirt over it. Make sure that both shirts are flat and lined up at the shoulders and neckline. 
Leave the t-shirt sleeves on both shirts untucked. [title] Trace along the edges of the well-fitting shirt.