want to remove a header
OK, so back on Broadway. You have a load bearing header, consisting of a pair of 2x10's with a filler above. Unless you are a structural engineer, know a structural engineer who is willing to do the analysis for you, or plan to hire a structural engineer, DO NOT replace a pair of 2x10's with a pair of 2x6's. That header appears to have been designed with a purpose, let's give the installer some credit, they might have known what they were doing, and perhaps sized the beam appropriately. Reducing to a pair of 2x6's will reduce strength drastically, and could lead to failure.