There is no path that goes directly from 3.4 to 4.2. In order to do this, you need to follow an upgrade path between versions.
I'd recommend upgrading:
- 3.4 -> 3.5
- 3.5 -> 4.0
- 4.0 -> 4.1
And so forth. You can consult the release notes for each one on how to do each transition, but in general you need to set the store upgrade setting to "true" in order to do this.
