You can just run a batch backup again which overwrites the previous backup.
The best way to do this on an ongoing basis though is to use the "schedules" option (unsure if this is a paid feature or not) and choose the schedule called "redo backups for modified data" and then set it to run as often as you want. I run that schedule twice a week offset a few days on either side of "backup all new apps and newer versions". That way once I have my main backup done, from then on its auto backing up new apps and their data along with modified data on all apps on an ongoing basis without me having to worry about a thing.
You could do essentially the same thing by using the schedule for backing up all apps and app data. The only downside would be taking longer to backup the whole 9 yards every time instead of targeting what you actually need backed up, which is new stuff and data changes you've made recently.