Under “Other Settings” select “Summary Widgets“. Then select the “Module” and “Check box” the default Summary Widgets you want to hide.
For this example I have hide the “Comments and Activities” widgets from “Organization Module“.
In order to hide unwanted default existing widgets you will need “VTiger Summary Widgets“. It works on 6.x and 7.x VTiger Open Source/community editions. This extension also supports few other actions such as create custom widgets and specify things like name of the widget, columns/fields to display, limit records (if needed) & enable or disable ability to create new records from within the widget.