To delete photos or videos from the timeline, check the images/videos you want to delete and click "Delete" in the bottom part of the screen:
Confirm that you want to delete the images/videos in the dialogue-box that pops up (or hit cancel if you changed your mind):
If you confirm the deletion, your photos will be removed from your timeline and any albums they were added to. The photos and videos you delete are stored in the Trash in your Jottacloud account for 30 days. Then they are permanently deleted.