How to rename a branch?

Question

GitHub

I want to rename a branch.
Everywhere it says that you need
git branch -m staroje-imia novoje-imia
git push origin --delete staroje-imia
git push origin :staroje-imia novoje-imia

Only after executing the second line the error [remote rejected] master (refusing to delete the current branch: refs/heads/master)
I immediately enter the third line after line 1, then go to the github site, put the renamed branch default there, and then I enter line 2.
How to check everything without going to the site and setting the default branch?