Downgrade jquery from 1.5.2 to 1.4.2
The jQuery Update module updates Drupal's jQuery library from 1.4.4 to 1.5.2. If you don't want version 1.5.2 then you just need to uninstall the jQuery Update module and everything will go back to normal.

If you want to use jQuery Update just to update the jQuery UI library to v1.8.11 it looks like you'll have to patch the jquery_update.module file directly, as the version numbers for the base library are hardcoded into the jquery_update_jquery_replace() function using this code:

switch ($version) {
  case '1.5':
    $trueversion = '1.5.2';
    break;
  case '1.7':
    $trueversion = '1.7.1';
    break;
}