You can rename an album from the Photos page in your Dropbox account.

To rename an album from the Dropbox website:

1. Sign into your account, and click on Photos from the sidebar on the left.
2. Click the album you want rename.
3. Click on the album name at the top of the page. It will change to an entry field where you can edit the text.
4. When you're done editing, hit Return or Enter on your keyboard, or click anywhere outside the field.