Go to settings > apps > all and find CMClient. Tap it and tell it to clear cache and force stop. Do the same to DMClient then restart your TF. Then go to settings > about and tell it to check for update at the top of that screen. Wait at least 3-6 minutes to get a notification.
What is your tablet model number, TF300T, TF300TG, TF300TL? So far, only the TF300T (not the G or L) have gotten the update.
Also, what is the tablet SKU (Settings - About - Build Number right after epad). Should be a 2 character code like US, CN, DE, WW, JP, TW, etc. Perhaps your SKU has not yet gotten the firmware update.
Also, when you do perform the update, I recommend that you back everything up and factory reset once the update is done. Once done, don't log into Gmail, or connect to the internet. Install your apps with a few reboots in between. Then connect to the internet, gmail etc. When you update your apps, do them a few at a time and reboot in between. The main reason I recommend this is to ensure that the device is running smoothly. Mine was running a little slow after the update so I did these steps as I saw them on another forum and it's really fast. Hope this helps