Tested solution for upgrading from xwiki-enterprise-hsqldb-1.2.2.zip distribution to xwiki-enterprise-hsqldb-1.3.zip:
1-copy the entire WIKI_HOME directory to a backup folder (apart from a couple directories, it's a just-in-case precaution);
2-unzip the 1.3 zip file xwiki-enterprise-hsqldb-1.3.zip to WIKI_HOME;
3-delete the newly created database (XWIKI_HOME/database), and replace it with the backed up database folder;
4-If you have modified a skin, apply those changes to the new distribution skin files.
Alternatively (not recommended), just copy your previous skin folder to the new distribution webapps/xwiki/skins folder
Thanks, Ricardo Rodriguez