Is it risky to update my Linux Kernel to latest stable version when running Ubuntu?

The kernels that are offered via the Ubuntu repositories are tested and likely to work properly with the version of Ubuntu that you are running, more likely than the latest stable kernel version. But things might break anyway because some new driver might not match your hardware or a present driver might not be supported by that kernel.

For this reason it is a good habit to keep two kernels in the system, the newest one offered via the repositories and a previous kernel, that works well. Then you can select the previous kernel from the grub menu, if there are problems with the newest kernel.

If you want to 'see' the grub menu in a single boot system, edit the file /etc/default/grub and run

sudo update-grub

according to the instructions at

help.ubuntu.com/community/Grub2/Setup#/etc/default/grub

GRUB_HIDDEN_TIMEOUT=

    No value entered after the = sign
    The menu will be displayed for the number of seconds designated by GRUB_TIMEOUT.