I have a Github repository that I forked from some other project several months ago. It is now several months later and the original master repo has changed. I would like to update my repo to reflect those changes. Is this possible in the Github web interface? Or do I just need to delete the repo and re-fork it?
You can try and reverse how pull requests happen.
If your code somehow conflicts or is not quite clean enough, then this will not work to update via the GitHub web interface and you will need grab the code and resolve any conflicts on your machine before pushing back to your fork.
It's gonna be easier.
How to update a forked GitHub repo with changes from the remote upstream repository
Instructions from GitHub Help:
Setup / Operation Instructions:
Open Git Bash (Windows) or Linux / Mac Terminal
If you have not yet cloned your repository, you must change to the working directory of your development folder and clone it to your workstation.
Change to the working directory of your forked repo on your workstation.
List the current configured remote repository for your fork.
Specify a new remote upstream repository that will be synced with the fork.
Verify the new upstream repository you've specified for your fork.
Fetch the branches and their respective commits from the upstream repository. Commits to master will be stored in a local branch, upstream/master.
Check out your fork's local master branch.
Merge the changes from upstream/master into your local master branch. This brings your fork's master branch into sync with the upstream repository, without losing your local changes.
If your local branch didn't have any unique commits, Git will instead perform a "fast-forward":
You will now need to push the commits to your fork.
If you are not already authenticated, it will prompt for your github username / password. Once authenticated the new commits should be pushed to your fork and visible on github.