There is a big difference between a contract and a covenant. In a contract, people exchange goods and services. Every sale is a kind of contract. In a covenant, however, people do not exchange things. They give themselves .
Marriage is a covenant.
When Christ died on the cross, He established an everlasting covenant with us. He gives us Himself in Holy Communion, and we give ourselves back to Him in obedience and love. The best place to renew your marriage vows is at the Mass each Sunday, where you will renew your covenant with each other at the same time as Christ renews His covenant with you. He will teach you the meaning of love. But that is not all we wish you.