Can I upgrade my pfSense through the web interface?

From PFSenseDocs

Yes, download the desired upgrade tgz file, then visit System -> Firmware. Click Enable Firmware Upload, and click Browse to select the file you just downloaded. Then click the Upgrade Firmware button. The firewall will reboot automatically after completing the upgrade.

Note if you're installing an image from the snapshots server, you will receive a warning that "The digital signature on this image is invalid." This is normal, the snapshot releases are built automatically and signing them requires manual intervention so none of the snapshot releases are signed.