I think you will be less likely to run into problems if you do a clean install of 8.10 rather than trying to upgrade. I've never tried to upgrade, so I don't know from experience, it's just what I have read. Just run the live CD and choose to format your existing 8.04 partitions when you do the install.
If you do want to upgrade, it should be fairly simple. Press Alt+F2 and you should get a Run Command dialog box. In that box, type
kdesudo "adept_manager --dist-upgrade"
That should update you to 8.10 directly over the internet (no need to download and burn the CD).