The latest stable release or upgrade can be downloaded at http://www.genexus.com/GeneXus-For-SAP-Download.
A preview of the upcoming stable upgrade is available at https://www.genexus.com/developers/DownloadCenter?,,,5481 and is updated almost every night.
Details regarding the previews are published at the following pages
Disclaimer: Not all of those documents apply to GeneXus for SAP Systems (e.g. those related to C# code generation)