Since this is posted in: Absolute Beginners Section, I would agree on what has been posted here about downgrading the whole Linux distribution. That is definitely the most easiest thing to do, but...

In case you want and feel you got the time for it: learn how to build and compile your own Linux kernel.

I've done it myself "some years ago" and it's a pretty cool experience in my opinion, because you get to deselect/select exactly the things based on your personal taste and opinion, and that means you can take out a lot of hardware support that you will never need, so that's nice and Ubuntu will never ever be able to this for you (well... at least not for free). So if you choose that, there's lots of good documentation from different places on how to do it. I would advice you to make a full backup of your Ubuntu system before attempting anything like this.

It is also possible to have multiple Linux kernels to select from at boot time if configured correctly and provided the disc space is enough where the linux kernels are stored. It's pretty nice.