Actually, Diane, the uninstall code is included in the install.sql file...

Just open the install-vXXX.sql and take a look at the first 7 lines which are actually uninstall code (in case you run the patch more than once).

But, to simplify things:
Code:
SELECT @ZXconfig:=configuration_group_id
FROM configuration_group
WHERE configuration_group_title= 'ZX Slideshow'
LIMIT 1;
DELETE FROM configuration WHERE configuration_group_id = @ZXconfig AND configuration_group_id != 0;
DELETE FROM configuration_group WHERE configuration_group_id = @ZXconfig AND configuration_group_id != 0;
Just run this from Tools->Install SQL Patches. As with any other SQL patches, make sure you backup your database before running it.

Re: uninstall vs. upgrade - I suggest you uninstall first and then install the latest version. There are some new files added and the admin settings have changed so it would be quite hard to upgrade if you're not absolutely sure about what you're doing...

Regards,
Leonard