Linux Kernel 4.0 codenamed 'Hurr Durr I'm a sheep' (it's not a joke :) has been announced by Linus Torvalds on the mailing list. 4.0 is not with some big changes but some small hardware support, driver improvements and bug fixes. There are more changes being given in this article below. If you want to upgrade to Linux Kernel 4.0 then you can follow this tutorial.
April 15, 2015