dead link on collections

hi all, my site is http://www.fotoefex.co.uk

ok main problem is I created a page called gallery with hyperlink list of all the page links to my collections,
so when I click for example gallery in the menu, I get the page gallery with the lists of my collections, then say click animals and that opens the animals collection of images up for viewing.

now there is a link above the images saying Collection/animals and if I click the word Collection I get a dead page come up and the url is http://www.fotoefex.co.uk/collections i’m guessing the link should read http://www.fotoefex.co.uk/?page_id=508 but can’t seem to find where I change this link.

can any one help with a fix to this please.
thanks

https://wordpress.org/plugins/sell-media/