Hello, The upgrades depend on what brand phone you have. The individual manufacturers put their own software into the upgrades. they will announce when the upgrades are ready to roll out. Just do yourself a favor and do a partition wipe 1st. this clears out temp and junk files which can interfere with the upgrade. Also do a cache clean. The you may have a better download and less problems! I hope that I can help.
So far, the only phone's that have received it are Developer versions or Google versions. Carrier versions in the US have not received it yet.
It's expected that HTC will be the first on the M8 phone specifically, as rumors are indicating a couple weeks, maybe even a week or so from now.