To change the name of a journal, you will want to go to Journals from your Dash screen.
Once you are in your Journals, you will want to drag your finger from right to left on the journal that you want to edit.
Dragging your finger on the journal name will give you the option to edit or delete the journal. Choose edit.
A small screen will pop up. On that screen you can edit the name of your journal. Press "ok" to save.