You can only delete pictures uploaded under the logged-in user name.
If you have changed your user name by editing your profile, only pictures uploaded with your new user name can be deleted. If you want to delete pictures uploaded under previous user name, you must change your user name back to the previous user name to delete them.
To delete a picture:
1) Tap and hold on the picture you want to delete.
2) From the right side menu, select delete (waste basket icon at the bottom)
3) Tap OK on pop-up window to finalize deletion