The instructions from this site should be simple: Follow the upgrade instructions that are supplied by IBM. — Tom

Firstly this is a Monkey presses the button upgrade…. meaning the update of software is easy. Domino will work (should) afterwards without any changes.The Templates will update on Admin4 and other system DB’s on Upgrade. Note that if there are customisations of these or realy old servers in your environment this could effect you. The Domino Directory will possibly be one of these to be done (to get new features to be visible).But build a test server – put your Data on it… and test test test

I want some steps before upgrading the server.

I want some steps before upgrading the server.
 
Not surprisingly, that’s a topic area in the upgrade instructions that are supplied by IBM. At first, I thought you were originally asking about the upgrade itself; now you seem to be asking about possible preparation steps.
 
Since we don’t know anything about your environment, we don’t know what you might want to do. The best advice is to follow the steps in the upgrade instructions that are supplied by IBM. Start with the ‘Planning’ phase.
 
We could copy the instructions here, but why would that be useful? We don’t know which parts apply, so we’d have to copy it all. The instructions are already available. For example, even though I don’t have a Domino Server, there is Upgrade Central: Planning your upgrade to Lotus Notes and Domino 8.5.x. There are many possible paths through there, but only you know which steps fit your environment.
 
Tom