How do change a redirect to be the main entry and the main entry to be a redirect?

I'm fixing something due to fan stupidity of someone rushing a film entry, but I don't know how to change redirects.

To edit a redirect page, you have to change the URL in the upper bar. Open a edit window for any given page, then change the parts immediately after "groupname=" (namespace) and "title=" (work name).

The basic approach would be to copy the source of the main page, then paste it into the redirect, removing that. Then just turn the original work page into the redirect.

Thanks!

But fuck, now I had this unwanted subpage I accidentally made (I redirected a page but mystyped Film to Fim), now Kamen Rider 1 has a Fim sub entry.

Throw it on the Cut List.

Seems like editing the redirect remove the Fim