Delete specific Time Machine backup via GUI
To delete a specific backup enter Time Machine by selecting that option from the time machine icon in the menu bar. Once inside Time Machine, there will be a stack of windows. Click on the up arrow to the right of the window stack. This will start leafing thru the stack of backups with the dates shown in the top section of the windows. Run thru the stack until you get to the backup you want to remove. With the window for this backup at the front of the stack, click on the icon that looks like a gear located in the top part of the window below the date. One option that appears is to delete the backup. Choose that selection to delete that specific backup.