Plugin Failed to Upgrade – Website won't appear

I was in the middle of updating my plugins (including a crucial one), but as my internet connection was slow and the server for my site is also old and slow, the plugin failed to download after 1 hour. I had to stop in the middle of it, which I think I’ve done before with minor plugin updates. But now the website simply won’t appear. The url appears to go through, but then it’s just a blank white page. Not even a “website not found” error message, just nothing. What can I do to fix the issue? How do I do it if I can’t access anything since not even the Dashboard will show?

Thanks,
Ruthie Osborne
Director, ArtWatch International