What is Overwinter?
Overwinter is the first network upgrade for Zcash. Its purpose is strengthening the protocol for future network upgrades. It includes versioning, replay protection for network upgrades, performance improvements for transparent transactions, a new feature of transaction expiry, and more.
How do I upgrade?
Keep your Zcash software updated, and you’ll be on the newly-upgraded main chain along with everyone else. You will not miss the network upgrade, unless you are running your own full node and have manually configured your client to continue running the old code.