the auto-install is supposed to take care of this (removing old deprecated IH image settings and properly registering the IH4 menu)
The instructions say

You MUST do a complete uninstall of the hacked up version of Image Handler3
I found no mention that the IH4 installer cleans up old db entries.
The first quote from Diva refers to situations where folks install IH4 into a zc150 store that contains remnants of really old (thus the reference to "deprecated") versions of IH. Sometimes when folks upgrade from an earlier version of ZC, they forget to uninstall their outdated mods first, or do partial uninstalls and miss some of the files, and that is what she was referring to there.


The second quote, from the IH4 instructions, refers to a hacked up and totally unsupported version of IH3 (vs. deprecated code from fully supported previous versions of IH).

This instruction was included in the readme so that folks who chose to randomly edit IH3 to make it work with ZC150 without regard to full functionality and/or security would be able to upgrade to IH4 without issue.

Hope that clears it up for you