Doing an update into the MyCloud from within Windows is not only possible, it's not an issue.
You have to enable SSH from within the WD menu of the MyCloud, and then you use a Windows program like Putty (putty.exe) to log into the MyCloud's Linux system. I have done a number of updates without issue. Then there are some documented procedures to follow.
My issue has been that it appears the Twonky update package for the WD MyCloud's Twonky has changed. So far I can't get anyone to advise about the changes to the packages. The board moderators don't seem to answer questions about much of anything anymore. It's really too bad.
You can find the available packages here:
http://www.twonkyforum.com/downloads/
You can find the latest release notes here:
https://docs.twonky.com/display/TRN/Two ... ease+Notes
I "think" (I haven't tried them yet) that the packages for the Twonky 8.2.1 for the WD MyCloud single drive unit are these (firmware version dependant):
WesternDigital MyCloud 02.xx.xx
WesternDigital MyCloud 03.xx.xx
WesternDigital MyCloud 04.xx.xx
I updated a WD MyBook Live (not the My Cloud please note) to 8.2.1 with no problems.
The package version I used to used for the MyCloud (single drive) for Twonky 7.2.8 was:
"Linux ARM little endian glibc 2.2.5" (file: twonky-armel-glibc-2.2.5-7.2.8.zip) (for Twonky 7.2.
So, for Twonky 8.2.1 it should be:
"Linux ARM little endian glibc 2.2.5"(file: twonky-armel-glibc-2.2.5-8.2.1.zip) (for Twonky 8.2.1)
but this didn't work. Twonky server wont start. So I went back to 7.2.8 on my MyCloud's. If you are running 7.2.9, then the MyCloud came with it from factory. It's not available as a general download. That being said, to get the updated version after the 7.2.9 to work you might have to buy the license (about $20). Your MyCloud running 7.2.9 is only licensed for that version that it came with. You have to buy a license beyond that.
You say you are on firmware fw ver 2.11.133, so in theory you would use Twonky 8.2.1 {WesternDigital MyCloud 02.xx.xx} but I can't confirm that until I try my own (I'm on firmware 04.xx.xx). No one here is saying anything about those 3 new packages.
If you update you firmware through the WD interface, then you will likely need one of the other of the 3 packages. Don't update the firmware if you really don't need it.
Hope this points you in the right direction.