I've just downloadet the newest build available for Dynamics Nav 2015 (build 51013) but the "cd" doesn't contain the Upgrade Toolkit? Where can I download it from?
Because NAV2013, NAV2013 R2 and all other previous versions are "out of support", no Upgrade Toolkit exists on the latest builds for NAV2015.
You can find the Upgrade Toolkit on previous builds for NAV2015 (e.g. build 45244)
Answers
You can find the Upgrade Toolkit on previous builds for NAV2015 (e.g. build 45244)