Depending on whether you right-clicked a group or the Remote Update node, exporting will write either all computers from the selected group or from all groups to the specified text file.
Removing computers from the list
You can remove single computers, all computers from a group or all computers from all groups:
Right-click a computer and click Delete or select a computer item and hit the Del button on the keyboard.
All computers from group
Right-click a group and select Delete All.
All computers from all groups:
Right-click the Remote Update node and select Delete All.
The text file used for imports and exports should be configured to the following format:
[Name of group]
[Name of next group]
Names in brackets describe the start of a new group whereas names alone specify computer names. To see an example of such a text file simply add a couple of computers to the computer list and export it to a text file. You can then use this file as a template for future imports.