Question

how to start over the instal from version 16 to 20

Answer 1

Here are the instructions for upgrading MultiChain from the install page:

1. Stop any running nodes: multichain-cli [chain-name] stop  (use ps -x to check for multichaind processes).
2. Follow the regular installation instructions, overwriting the older executables.
3. Restart any nodes required: multichaind [chain-name] -daemon