CiviHR 1.1 requires CiviCRM 4.4.3+.
If you have an older version of CiviCRM, first upgrade CiviCRM to 4.4.3 or above. (Please follow steps mentioned at: http://wiki.civicrm.org/confluence/display/CRMDOC/Upgrade+Drupal+Sites+to+4.4+-+Drupal+7 )
Make a backup of the CiviCRM database.
Download CiviHR 1.1:
cd </path/to/extension/dir>
(ex: $drupalroot/vendor/civicrm or $civiroot/tools/extensions or a custom-configed path)
rm -rf civihr
wget https://github.com/civicrm/civihr/archive/1.1.0.zip
unzip 1.1.0.zip
mv civihr-1.1.0 civihr
Goto 'Administer => System Settings => Manage Extension' and click the "Refresh" button.
Notice the CiviCRM popup alert. Click on "Execute the updates".
Install the new CiviHR extensions: hrcase, hrim, and hrprofile.
If you use drush, you can install the new extensions on the command-line:
drush cvapi extension.install keys=org.civicrm.hrcase,org.civicrm.hrim,org.civicrm.hrprofile