Yeah, when Grub menu comes up, select your kernel (if it's not selected already), press 'e' to edit the section, hilight the line that starts with word 'kernel' and press 'e' again to edit it, then replace the word 'splash' with 'nosplash' or if it doesn't exist, write it there between the options. Press Enter to apply changes and 'b' to boot. Now the graphical bootup should be gone and you should see boot messages instead - if this worked, after the machine booted you can make the changes permanent by editing Grub's menu.lst as root:
sudo gedit /boot/grub/menu.lst
locating the same kernel line you edited from within Grub, and replacing 'splash' with 'nosplash' there. Save and exit, and you're done.
If there is something making the boot slower, it should be displayed now in the boot messages. If something doesn't look all right, start searching about it in here..
Upgrading trough the package manager is not recommended (by me), but it's supposed to work - at least for the Ubuntu packages. If you have non-Ubuntu packages installed, they might fail. Safest to do it with X closed, with apt-get and some manual editing of the source lists..you can do it from X too, but if the graphics card fights back after reboot, you need to edit /etc/X11/xorg.conf, possibly replace the used driver (Driver line in the section "Device" where your gfx card is mentioned) with "vesa" which is a generic driver, try to start X again, and if it starts, re-run Restricted Drivers Manager (if you've got one of those gfx cards - namely ATI or nVidia - whose drivers you installed from here) or manually reinstall your graphics card drivers.
Note that if X doesn't start after upgrade, don't right away reinstall, but rather hit CTRL+ALT+F1 and see if you can login in text console. If you can, you're set