This article is from Github’s help page here I am adding it here to quickly reference it when I inevitably forget how to do it.
If you don’t have push (write) access to an upstream repository, then you can pull commits from that repository into your own fork.
Change the current working directory to your local project.
Check out the branch you wish to merge to. Usually, you will merge into
git checkout master
git pull https://github.com/ORIGINAL_OWNER/ORIGINAL_REPOSITORY.git BRANCH_NAME
If there are conflicts, resolve them.
Commit the merge.
Review the changes and ensure they are satisfactory.
Push the merge to your GitHub repository.
git push origin master