Upgrade from 3.13 to 3.25.1-04 steps


we are planning for upgrade from 3.13 to 3.25 are there any steps for upgrade plan.we did couple of times in test machine but every time we see some different error.
Let me share you the steps we are following the doc as per KB.
we would like to know once we do upgrade will not we revert this back to older version if we just revert the nexus-data dir which is karfa.data.
when we try to go to early version we are not able to see any repo also in blob it as 0 size.

can anyone help in this upgrade