Assets Tab & Save

To purge your Project file of all extraneous assets, click on the Assets TAB. This tab shows you an itemized list of all of the assets currently contained in your Project file. Among these assets you will notice a file called index.xml. Never delete this file as it is required (we should have hid it so you couldn't but oh well...).  If you see a file you did not create personally (other than index.xml - which we should have hid), then it is garbage and ought to be deleted.Once you have finished deleting files from the Assets tab, SAVE your product so that you save the changes. Do not hit Apply Changes as this will only bring all of your deletions back and you will have to do the whole thing over again (I know, you're probably thinking why does Apply Changes revert my changes...honestly I have no idea).
Add or Delete
When Deriving from a product that contains more Material slots then your own you may end up with unnecessary files in your final exported Project file.  To remove these unnecessary files, select the file in question and click the Remove button.  If you Remove materials, please make sure that the Material/.xrf file you are using contains a Sub-Materal whose name matches the Material ID number in the window. If the Project file you started with contains more materials than you need, you should delete the excess to make your Project file size as small as possible.

There are four steps to deleting those extra files:

1. Delete the material reference in the Meshes TAB
2. Delete it's corresponding .xrf file in the Assets TAB
3. Save your Project file
4. Apply Changes