Oracle 11.2.0.3 to 11.2.0.4 I'm planning to upgrade 3 instances of Oracle (all same Oracle Home) from 11.2.0.3 to 11.2.0.4. I'm going through the installer and I get to the question about Upgrade or install just the database software. I only want to upgrade one instance initially and leave the others running on 11.2.0.3 in parallel. My question is, what's the difference between:

Install database software only
Upgrade an existing database

I really don't want to touch the other SIDs on there.
Choose Install database software only, then later you can upgrade your databases one by one with DBUA (Database Upgrade Assistant) from the new Oracle Home, or by performing a manual upgrade.