What is the files size of android update?

As Lollipop 5.0 is a whole system update, rather than something incremental, could be anything from 400MB to over 1GB, all depends on the make and model of the device. The time all depends on how quick the manufacturer, and sometimes carriers, gets their Lollipop 5.0 updates out, which won't be available for all devices of course, usually it's recent ones from known reputable manufacturers. If you have a carrier customised and subsidised phone, then it will often take longer, or not at all. Existing Nexus devices should get it first, because those updates come direct from Google.

"Software update" in notifications generally means an Android system firmware update. But you'd have to look at the update itself, which should tell you the nature of it and what is being updated.

For the Oppo Find7, the Color OS 2.0 update, it's 950MB. Although not Android, the iOS 8 update for iPhones is 1.1GB, and apparently some users have had problems with that, because it requires at least 5GB of free space on the iPhone or iPad to apply the update.

 

Software updates that are just bug fixes can be as small as 10mb. The biggest I've experienced I think was nearly 2GB from Android 3.1 Honeycomb to Android 4.0 ICS on my Tab Plus. Granted though that came with an entirely new TouchWiz version which was pretty big.

 

It is not possible to update my android with this huge file size.