This update adds an all new free character: Rocco! It also adds two new skins: Shinobi Rocco and Sun Wukong Skree. And of course a series of balance tweaks, fixes and improvements. Especially Lonestar and Voltar got a lot of tweaks this patch. Have a look here for the complete patch notes:
https://www.awesomenauts.com/forum/viewtopic.php?f=6&t=39493
If the patch does not download automatically for you, try restarting Steam or even your computer until it does.