The question is quite that what is in the title:
If $R$ and $S$ are homeomorphic Riemann surfaces, is it true that always exists a homeomorphism $h:R\to S$ which is orientation-preserving (at least in the case in which $R$ and $S$ are closed Riemann surfaces with genus $g$)?
Notice that this is equivalent to the question:
And the answer to this is yes. All compact orientable surfaces admit an embedding into $\mathbb R^3$ which is symmetric with respect to the $xy$ plane, and you can consider the reflection on that plane.