Turn the sofa upside down and examine how the legs are attached. If the legs have screws, remove them by unscrewing all the screws. Alternatively, twist each leg off if the legs screw in with a bolt.
Center each T-plate over the hole left by the former sofa leg, if the legs you removed were bolt mount -- the type with a center bolt that screws into the base of the sofa. Use screws to secure the T-plate. Screw the bolt of a new tapered sofa leg into the T-plate by twisting the leg by hand until the bolt is fully inserted. If the former sofa legs had a different mounting method, such as a universal leg with regular screws, use a drill to center a hole the same size as the new bolt-mount legs -- usually 5/16 inch -- before installing the new legs.
Repeat for each leg. Turn the sofa upright.
Cover the sofa in a close-fitting slip cover without a skirt to copy the style of a sleek vintage sofa. Add colorful accent cushions, such as thin, rectangular cushions to fit the sleek style. Choose cushions that coordinate with the slipcover color.
Cover a bulky sofa with a skirted slipcover in a fabric that suits a vintage sofa, such as a pastel, nubby fabric or red for the '50s, a bright geometric design for the '60s or jewel-toned velour for the '70s. Cover the entire sofa, with the seat cushions in place, to give the sofa a unified appearance.
Tuck the sofa cover in neatly between the back and the seat cushions and next to the arms. Tucking extra fabric in will help give the slip cover a better fit. If the sofa cover has any straps, snaps or other fastenings, use them to customize the slipcover to your sofa. Adjust the slipcover so the dust ruffle or skirt just touches the floor.
Arrange vintage cushions on the sofa to complete the transformation to a vintage sofa. Add matching or contrasting accent cushions that fit the color scheme, for example brown, purple, avocado, lime or burnt orange velour for the '70s or India print cotton cushions for the '60s. Line cushions up across the back or lean two cushions against each arm.