updating old .htm files on a server to .html files – simplest method please

Hi, I’ve inherited an old website, all files on server are .htm. I’ve completed some html courses and have started to update the pages. When I tried to transfer new (.html)files to the server they aren’t replacing the old (.htm) files.
Is there a method to replace all the files? How does this effect all the hyperlinks?
I have a window 11 laptop. I’m using Visual studio code .
Courses used www.w3schools.com and HTML 101 Kalob Taulien.
I have basic knowledge and learning as I go along – or using courses to correct any errors.
Grateful for any assistance please.