1) Obtain a community consensus on the change.
I have X amount of bitcoins in my wallet. Am I part of the community?
Actually, that's a very interesting question. From a technical standpoint, you only need the consent of the active miners. From a practical standpoint, you mostly need the consent of those managing the reference client.
Theoretically, a disagreement between a large group of miners and those maintaining the reference client could lead to a fork where the public hash chain splits into two incompatible groups of programs, each rejecting the other's hash chain, where everyone with bitcoins prior to the split has them in both systems (and could spend them differently in each system). However, letting that happen is in nobody's interest. So it's extremely unlikely.
Where can I read about the procedure to be followed when a community consensus for a change need to be obtained?
In the post you are replying to, which you already read.
You need all stakeholders to agree to the change. Although practically it is the client implementors and not the miners who decide which way to go, after all a miner isn't going to use a protocol nobody accepts as being valid.