Unable to change keywords in custom fields

Hi guys,
my first post here.

Ive got a new site with all in one SEO running. I have had someone set up some new pages for the site, and hes added the same keywords across all the posts. When i go to edit the post and remove or change the keywords, then click ‘update post’ the keywords stay the same, and the custom keyword field still has the original keywords listed. How do i get round this issue ?

Any suggestions please im new to wordpress.
Thanks
Marc