The Journal is divided into two main sections:

All Journal logs arrive in the Events section. If you don't want to lose a message as a result of the automatic deletion of older Journal entries, you should mark the entry as "Important" by pressing the star button in the top right corner of the Journal entry. Doing so will move the entry from the Events section to Saved.

 

You can delete Journal entries by pressing the Delete button (the red cross), which is always visible in the top right corner of the entry, next to the Copy and "Mark event as saved" icons.