Key renewal when the sequence counter is only 32-bit
The standard rule is simple: Re-key whenever the sequence counter would (likely enough) repeat. For incrementing sequence counters this should be the case when they overflow.
If you're using AES-GCM and you were to pick the (96-bit) nonces randomly, re-keying after $2^{32}$ messages would be recommended. However given that you appear to use an actual counter and feed it into GCM's nonce input re-keying on wrap-around is good enough - which incidentally for 32-bit counters would also happen around $2^{32}$ messages.
If you used a 64-bit counter, the previous thought would extend somewhat and a re-key would be required at last every $2^{64}$ messages. However for reasons of the security proof you should really re-key after hitting $\sigma+q=2^{48}$ with $q$ being the number of nonces encrypted and $\sigma$ being 1/16th of the total number of bytes encrypted while not encrypting more than 64GiB per nonce-key pair.