You don’t say where you are located (city, state) so giving general advice would be risky. You should contact an architect or structural engineer who is familiar with the building requirements for your area. If your location has earthquake, tornado or hurricane risks, then there will be more stringent codes to comply with.
A professional designer can also estimate the 2nd floor loads that will be carried down to the header and support posts. You don’t say whether you have a fiberglass shingle over plywood roof, or a a clay tile roof. Or if you have a cast-iron bathtub or a carpeted hallway directly above your load-bearing wall. In other words, the loads from the 2nd floor have a great deal to do with the proper removal and redesign of this interior wall.
Another consideration is that your homeowner’s insurance may reject any claims that you make in the future if you decide to design this project yourself without proper engineering or pulling building permits.