Hmm... So, you have Lubuntu 18.04. I have (almost - mine is 64 bit) the exact same OS on this computer.
However, you have a 32 bit OS installed. You have the last of the official Ubuntu LTS 32 bit OSes.
I do not get that message, so I think it's safe to conclude that it's a 32 bit-only message. I didn't dig through blog posts, but there was probably some sort of announcement leading up to this. It seems to indicate that there will be no more official 32 bit support.
So, the next logical question is:
Does your hardware support 64 bit?
If it does, and you want to stick with Ubuntu, download a 64 bit OS. If you like Lubuntu, that's at
https://lubuntu.me.
If your hardware doesn't support 64 bit, then I suggest moving away from the Ubuntu family of flavors. A light 32 bit OS can be something like MX Linux - which is really quite a nice OS.