how are you?
I want update to kernel 4.9, but I not know if this can cause problems in my computer.
You can always try to upgrade you kernel.
However, as there is no 4.9 kernel package in elementary OS, you should understand the risks (as in: your system will not boot any more or there will be driver errors; there is only a very small chance of danger as in actually bricking it).
If you are sure to go on with the upgrade, I would start at http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.9/
I was able to install 4.9 on my machine without issue. I used Ukuu which makes the process fairly painless and allows you to easily revert back if you have issues.
I had update my kernel to 4.6 trying to fix some flickering in chrome caused by skylake intel processor but not success. I think you can upgrade to 4.9 carefully.
I have two machines on Loki - one running latest 4.8 and other 4.9 and both run. As long as you use the Ubuntu packages, your old kernels will still be bootable via Grub.
Yeah I upgraded to 4.9 on my skylake laptop with no issues at all. As others said, you retain the ability to boot from the stock kernel with grub.