The latest download can be downloaded from IPS if you have an active customer badge.
If you can't you can download it from http://icelabz.net/sitemap/
once downloaded, upload the files to your forum's root folder.
then login into the Admincp > click Manage applications & Modules
there you will see upgrade next to sitemap click it and follow through the installation.
The latest files is Sitemap 2.3.5
If you need further help please let me know