Automorphisms of the group $Sp_n$ ($n\leqslant4$) over a semilocal rings

Let $R$ be a commutative semilocal ring with invertible elements $2$, $3$, $5$ decomposable in direct sum local rings. It is proved that all automorphisms of the symplectic group $Sp_n(R)$ ($n\leqslant4$) are standard.