The https://wiki.ubuntu.com/Kernel/LTSEnablementStack page has the appropriate upgrade command in order to upgrade the kernel to the newer and supported version.

According to https://wiki.ubuntu.com/Kernel/LTSEnablementStack#Kernel.2FS... you are now at the Linux kernel 4.4 and it will remain the same until the EOL of Ubuntu 14.04 (in 2019).