how do i unlock my dead uncles iCloud account?

The only way that you may be able to get the Activation Lock removed is if you provide a Death Certificate as well as the original proof of purchase for the device. Take them into an Apple Store. They will have to determine if they have enough info to de-activate the Lock.

Best of luck,

GB

Beyond what I have provided for you, I do not know of any other way for you to have the lock removed. Where did your Uncle purchase the device?

GB