Open any Finder window on your Mac
Look for the Time Capsule icon under the Shared heading on the left side of the Finder window
Click on the Time Capsule icon and a folder named "Data" will appear in the window to the right (unless you have changed the name of the drive)
Double click on Data to open the drive. You may be asked for the Time Capsule admin password the first time that you do this
You will see two separate files with the name of each Mac that has been backing up
Carefully click to highlight the name of the file whose backups you want to delete....to highlight the file
Click the gear icon above the window
Click Move To Trash