How a sofa comes apart is dependent on two things --- how it was put together in the first place and why it is being disassembled. Sofas that will be reassembled should be carefully taken apart. Disassembly should generally follow the building of the sofa, but in reverse. Traditional sofa building requires the frame to be padded before upholstery is put into place. More contemporary sofas may be modular in nature with upholstery created as a unit that snaps into place. Sofas trapped in a room and needing to be removed may simply require the removal of the legs or arms.
Remove any loose cushions and set them aside.
Turn over the sofa if needed and assess how it was put together. For metal-framed or modular sofas, make an educated guess about what the last piece to be attached was and begin by removing that piece. Slipcovers are easily removed and may reveal original upholstery underneath.
Remove upholstery, padding, strings and any burlap covering that might have been used during the upholstery process. Use a sharp box or mat knife. Pry off zigzag springs. Upholstery fabric that will be reused for another project can be removed carefully using a seam-ripping tool to break the stitching.
Look the sofa over once the frame is bare and easily viewable. Note what type of connector was used to put the frame together and locate the tool(s) needed to disassemble them. Sofa frames are typically put together using nuts, bolts, screws and large staple or nail guns.
Consider cutting wood frames in half using a reciprocating saw, instead of taking them apart piece by piece. This method works well if the sofa is to be reassembled elsewhere. Consult a professional woodworker about what is required to reassemble the sofa safely before making this decision. All upholstery will need to be removed, including springs, before cutting the frame in half. Professional services are offered that remove the upholstery, saw the sofa in half and reassemble it in a new location. Check local furniture repair and upholstery shops to find out if they offer this service and ask to see their work first before agreeing to this method.