Updates were rejected because the tip of your current branch is behind hint: its remote counterpart. Integrate the remote changes (e.g [duplicate]

Answer 1

You need to merge the remote branch into your current branch by running git pull.

If your local branch is already up-to-date, you may also need to run git pull --rebase.

A quick google search also turned up this same question asked by another SO user: Cannot push to GitHub - keeps saying need merge. More details there.