Make sure you understand and follow the instructions in Preparing to Upgrade to 4.9.2.
Then start with the section where your current version fits. For example, 4.2 fits between 188.8.131.52 to 4.5.
Identify any steps that don’t apply.
For example, Retain 4.2 should be running the new Retain 4.x indexer, so you would skip the re-indexing process.
Use the instructions that follow to upgrade your system to Retain version 4.9.2.