Adding filters will allow you to deselect certain items from your backup
Login to the client and select "backup sets"
Select the backup set you want to add a filter to and navigate to "source"
Turn "filter" to on and press "+ add new filter". From here you will be able to name your filter and edit the filter to do what you wish.
The blank filter form looks like this
Here is a filter I have created so that .mp3 files are excluded from the backup, If your backup is for certain files it is best to put the location in the "Apply this filter to all files/folders in" and select "this folder only" - else the software will scan all the folders. Press "ok" and "cancel" - If you don't want to add anything else to the filter.
Press "save" and exit out of the panel if you have nothing else to do in the panel.