How to change the name of a gist in github?

Considering the order of files within a gist is asciibetical, you can try and add one file in uppercase.

That file will come before any other and will define the name of your gist.

Note that it won't change the url of said gist, as explained in "Namespaced Gists".

Even better, you can add a file with a leading space in its name. It's virtually invisible and gives you more freedom when choosing the title and names for the files: