A complete conformal metric of preassigned negative Gaussian curvature for a punctured hyperbolic Riemann surface

Let $h$ be a complete metric of Gaussian curvature $K_0$ on a punctured Riemann surface of genus $g\ge 1$ (or the sphere with at least three punctures). Given a smooth negative function $K$ with $K=K_0$ in neighbourhoods of the punctures we prove that there exists a metric conformal to $h$ which attains this function as its Gaussian curvature for the punctured Riemann surface. We do so by minimizing an appropriate functional using elementary analysis.