  In this paper, we establish the existence of conformal deformations that
uniformize fourth order curvature on 4-dimensional Riemannian manifolds with
positive conformal invariants. Specifically, we prove that any closed, compact
Riemannian manifold with positive Yamabe invariant and total $Q$-curvature can
be conformally deformed into a metric with positive scalar curvature and
constant $Q$-curvature. For a Riemannian manifold with umbilic boundary,
positive first Yamabe invariant and total $(Q, T)$-curvature, it is possible to
deform it into two types of Riemannian manifolds with totally geodesic boundary
and positive scalar curvature. The first type satisfies $Q\equiv
\text{constant}, T \equiv 0$ while the second type satisfies $Q\equiv 0, T
\equiv \text{constant}$.
