A load bearing wall supports the weight of additional floors and roofs. A simple way to determine whether a wall is load-bearing is to look in the attic for the direction of the joists. If a wall is running parallel to them then it probably isn’t load-bearing, while if it is running perpendicular to the joists it might be or should be treated as if it is. If you can’t tell if a wall is load-bearing have a structural engineer look at your house’s structure.
Some load-bearing walls can be replaced with beams. It all depends on the weight and span of the load. All support beams are rated according to their load and span capacities, and most lumber yards can tell you what size beam you will need.
Remove everything from the room being renovated and cover the floor surface if it is in good condition and needs to be protected.
Place a two-by-four stud against the ceiling, parallel to your load wall, approximately three feet from it. You may need a friend on another ladder to hold the stud up. With your nail gun, nail the stud to the ceiling in at least three to four locations spaced evenly across the span. You should be nailing into your ceiling joist through your drywall or sheetrock/plaster.
Fit the other end of your temporary wall using the same technique, installing studs every 16 inches or less. This wall will carry the load of most standard walls. You are simply duplicating the existing support wall under the same load. Install any extra post supports as needed if your engineer told you to do so.
Toenail and/or use plate supports to secure your beam to the posts and joists. Carefully remove your temporary wall so that you minimize damage to the ceiling and floor.