Stupidly having being unable to access PhpMyAdmin is resorted to Fantastico to update my gallery but i didn't have enough space on my server to complete the upgrade so after a long time with my host i managed to upgrade it finally
firstly i had an unexpected error which i fixed by upgrading manually
then guests wasn't allowed access to galleries which i changed in groups
but one thing i cannot fix is the admin navigation is vertical (see image) and is consistant through all themes
http://thepricey.co.uk/gallery
You need to review the changes required for your custom theme.
Please read your docs.
As Joe already suggested, either use a theme that has been designed for cpg1.5.x or upgrade your theme as explained in the docs: http://documentation.coppermine-gallery.net/en/theme_upgrade_14x-15x.htm