The starter is located under the intake manifold, and you will have to remove the intake manifold to get to it. Do not forget to buy a intake gasket before you take it off, because they always fall apart when you take the intake manifold off.
Remove the intake manifold retaining bolts on your 2003 Chevrolet Malibu. The manifold will come off. Remove the manifold gasket and clean the surface. Put the new manifold gasket on and reverse the process.