Simply navigate to "Releases" on the right side of the page, download links for the compiled JAR as well as the corresponding source code are under the "Assets" category below the changelog. Make sure to review all changelogs when updating!
This software is licensed under the GNU Lesser General Public License version 3. In short: This software is free, you may run the software freely, create modified versions, distribute this software and distribute modified versions, as long as the modified software too has a free software license (with an exception for linking to this software, as stated by the "Lesser" part of the LGPL, where this may not be required). The full license can be found in the LICENSE and LICENSE.LESSER files.