Here is how I would procede, given that this is not a production server that needs to be available at 99% time. In general, I would install 12.04 from scratch on another partition and see whether the new setup works. The problem with updates between an ancient and modern release is that you can break a working system without getting the desired outcome. The problem with step-wise upgrade is (i) the more steps, the more opportunity for something to go wrong (ii) takes a lot of time.
- Backup your data and system configuration.
- Make sure the backup has worked (this is an often neglected step...)
Make sure that all your data are on a separate partition.
If your data are on the same partition as the system, then you need to resize it, create a new partition for the data only, move your data to this partition, create links and fstab entries such that the new partition is mounted in the correct place and that your system works as before.
Create an extra partition for the new system (12.04) without destroying the previous system.
- Install 12.04 to the new partition. Mount your data partition, create symbolic links if necessary. Find out whether the new system works, tune it etc.
- If the new system works, keep it. Otherwise boot to the old system, and go to askubuntu.com with a new question.