If I want to change the filename, can I just write nano ~/Desktop/commission2.bpmn?

The command nano ~/Desktop/commission2.bpmn will open the file commission2.bpmn in the nano text editor, but it will not rename the file.

To rename a file in Unix-like systems, the mv command is used:

mv ~/Desktop/oldname.bpmn ~/Desktop/commission2.bpmn

If a file with the new name does not exist, it will be created with the new name, and the old file will be deleted (effectively renamed).

Therefore, to rename a file, you should use mv, not open it in nano.