Please read the release notes at https://github.com/JoinMarket-Org/joinmarket-clientserver/blob/master/docs/release-notes/release-notes-0.8.0.md for details on what this release includes.
This is a significant upgrade - Joinmarket now uses native segwit (bech32 addresses) for coinjoins, by default.
You're strongly recommended to backup, and then recreate your joinmarket.cfg (in ~/.joinmarket by default), to make sure you have the latest version of the config settings. Then read the above release notes which will guide you on what changes may or may not be needed for your situation.
Please verify the PGP signatures of the releases (zip files and exe file, see below) before using. They are signed with AdamISZ's pubkey (fingerprint: 2B6F C204 D9BF 332D 062B 461A 1410 01A1 AF77 F20B.
A reminder that since 0.7.0, (gpg signed) Windows executable builds of JoinmarketQt are included with the release. (Similar binaries for Linux and Mac are not provided but may be if people show interest in testing and working on it.)