I’m unable to update ios 14.8 and every time i try in the end download fails

You can't install 14.8 anymore now that iOS 15 is avaliable.

Go to Settings - General - iPhone Storage - check here for an iOS 14.8 update file. Delete the file. 

Restart and see if the iOS 15 update is now available.

Yes you can. You will need to turn off Low Power Mode to install the update.

To update all of these requirements must be met:

• You must be connected to a Wi-Fi network (and not a personal hotspot) unless it is an iPhone 12 series with an active 5G network connection
• The phone must be charged to at least 50%, and preferably plugged in so it stays above 50% during the update
• The phone must not be in Low Power Mode
• The phone must not be connected through VPN
• The phone cannot be in Airplane mode

How do I do this? I’ve tried all of Apple’s suggestions and nothing is working.

Have you got this to update yet?

I have the same issue but low power is not on.

Do you resolve the problem? I have the same problem with you on my iphone X when update ios 14.8

FYI, for me it was a matter of capacity. As soon as I cleared some memory, it installed. Give it at least 6-10 GB of open space.