Downloading the newest version of MDK-ARM is no problem just go to the KEIL Download Page.
There you find the newest Version as Eval Version. Then you can install your license and use MDK-ARM as always.
Older versions can be found under Maintenance Status and Previous Versions. Therefore you need a license which supports the version you need. This works fine when you have a Node-locked or Floating License. But when you have a FLEX-License your key will not work, because the FLEX key comes from ARM and not from Keil.
To download MDK-ARM product updates (or previous versions) with a Flex license use the following easy Workarround.
Hint: With a FLEX-License you can only use MDK-ARM 4.60 or newer.