If you upgrade before the hardfork
Install a Bitcoin Knots version that includes the BLAKE2b change. Downloads will be on bitcoinknots.org when that version is published; source is at github.com/bitcoinknots/bitcoin. Keep your existing Bitcoin data folder. Set the announced blake2b_headline in your config. You do not need to download the chain again or move your coins.
If you switch after the hardfork
Your current node software may have followed the legacy SHA256d chain. On startup, this release usually notices those extra blocks, walks back to the fork, and then downloads the BLAKE2b chain.
A pruned node deletes old blocks to save disk space. If you waited so long that those walk-back blocks are already gone, rebuild the node and download the chain again.
Everyone
- You do not need to move your bitcoin before the fork. Coins created before the fork remain spendable.
- After the hardfork, Bitcoin Core and older Bitcoin Knots still use the legacy SHA256d algorithm and follow a different blockchain. Today's ordinary Knots download is not enough; you need the BLAKE2b version.
- Miners should use DATUM against a Knots node. Wallets and exchanges have additional work; see the FAQ and businesses page.