GIT: Bitbucket delete master branch

 

git - Deleting remote master branch, refused due to being the current branch - Stack Overflow

Note: for Bitbucket, you would change the default branch by accessing the settings of your repository, and changing the branch at the "Main branch" combo box.

Once the main branch is no longer master, then you can push and remove master.

MarsAndBack confirms in the comments this applies to GitHub as well.