Redirect page-links

Anyone who knows how redirect the page-links in the header menu (above the header.jpg) and in the sidebar widget?

I’ve created a webshop outside wordpress and want it to be linked in as smooth as possible, hence I want to redirect a current page-link.

You can see my page at at https://www.fotokunstner.no, the link I want to change is the one called “NETTGALLERI”.

Hope you understand what I mean.