Yes! And you don't want to just delete duplicates. If you delete an item that was previously cited in a document, it will break the link to your Library (even though an "exact duplicate" still exists).

So, follow the instructions here: https://www.zotero.org/support/duplicate_detection

Edit: Oh, and note well, the algorithm for determining duplicates isn't perfect. False positives do occur. This is actually a complex task. This is a known issue and is on the Devs radar. So don't just blindly click merge.