It would be good to know what you are running now. Open a terminal
(Applications, Accessories) and type: lsb_release -a

You can also find out from Firefox at Help, About. We don't need the Firefox
version, just the Ubuntu version. There is an upgrade path that you must
follow. If you are running 8.04, for example, you must upgrade to 8.10
before upgrading to 9.04, the latest version.

Report the output back to us. If you are running an older computer, then it
may or may not be wise to upgrade. There are inherent risks with any
upgrade. If you use wireless networking then the card may or may not work
afterwards. Video is a big problem with 9.04, especially with Intel
chipsets. This is not due to Ubuntu itself, but the way the new kernel now
handles graphics and a new driver is needed and Intel in particular has been
slow to produce them. It is good to know what you may be getting in to.