To summarize, there are 3 resource files to edit:

EditEvents (uses this for event edit form), modify "lblCustomField1.Text" and "lblCustomField1.Help"

SharedResources (uses this for event details), modify "CustomField1.Header" and "TokenCustomField1Label.Text"

Settings (controls the labels in the Settings when you are configuring the module.  Don't have to change if your user won't be modifying the settings.), modify "CustomField1.Text"

You access these from the Admin menu:

Admin | Languages | Local Resources | Desktop Modules | Events | App_LocalResources

Make sure to choose the "Portal" option mode unless you really want to change them at the host level (i.e., for all portals).

And, make sure to save the resource file before navigating to another page or your changes will be lost.

Hope that helps.