Before doing this(i.e. adding the next month to the dropdown menu) process the 1st set of photos for the month up to and including Setting the Featured Image
Go to Dashboard
Make a new page, Pages - add new
Enter a title, eg November 2016 Walk Photos
Click Page Builder faint tab
Choose Blank Layout template
Row layouts. Drag 1 column into centre
Drag Saved Rows - Group Galleries across
Put the correct month in where it says "Month 2016"
Add Content (above)
Saved Rows - Title+Previous+Next - drag into top box
If you get a blank box between Title and Slider press X to delete it
Alter Month from July to November or whatever. Save
Add the first walk on the slider and delete the Castle Combe one.
Add the first walk to the right hand side of the page.
Done. Publish changes
Customise (at top) to get the new page in the menu. Main menu. Add items, pages select page, click reorder. Use Up arrow to get to the right group then side arrow to insert in right place. Save and Publish.
Put in links from this month to previous month and vice versa in the usual way.
Link the new photos to the previous photos and vice versa in the usual way.