I have an old Acer netbook which is running Lubuntu 14.10. I haven't used it in a while and after booting in it is prompting me to upgrade to Ubuntu 15.04. If I go ahead with the update will it upgrade to the full version of Ubuntu, which I doubt will run well on old hardware, or will I get to keep Lubuntu?
It will upgrade to Lubuntu 15.04, not Ubuntu 15.04. It will not replace LXDE with Unity (The differences between any flavor of Ubuntu is the desktop environment, so literally Ubuntu is the same as Lubuntu, only with Unity instead of LXDE.) Also, upgrading can have good effects, such as:
- Better security
- More features
- More useful stuff
So, you should go upgrade it, and 14.10 is old and end-of-life now.
Here's an image to show it's old and end-of-life: