In order to install a new version, do I have to uninstall the old version? Or can I just use the new config and skin? Thanks.
My experience has been to remove the old version first and then install the new version. I have had to best success upgrading doing it this way.
I recommend backing up you config and skin (assuming you have tweaked and not renamed the slider skin) prior to uninstalling TodayPlus. After, installing compare the old and new config files, sometimes some of the items format change.
Your old skin should work however; there was a major change to the POOM section for v0.10.0 (some settings are now in the skin and config instead of all in the config file for older versions).