Well, highlighting messages does not delete them. What is the "this" and the "that" that you tried?

I’ve also tried reinstating them from the deleted box and then tried to delete them that didn’t work so I deleted them from the deleted box and still didn’t work. They just don’t want to seem to leave my screen

I am asking: How are you trying to delete them? We cannot know what is not working if you don't tell us.

There are many ways to delete messages after selecting the ones that you want to delete, e.g.:

• Click on the trash can icon.
• Press the <delete> key on the keyboard.
• Drag messages to the trash can.

Probably more important: These are only old messages, right? Try this:

1. Back-up your Thunderbird profile.
2. File (menu) > Compact folders
3. Right click on the inbox in the folder pane. Select "Properties", then "Repair folder". Give it a little time.

Excellent, thank you very much. That worked clear screen.