I want to download update with hotspot

You must have a stable Wi-Fi connection.

Or connect to a PC with the latest version of iTunes installed.

Charge the battery to 50% or higher.

Don't use a Hotspot.

Don't use VPN.

And make sure you have enough free space.

You cannot do this.

All major Apple software updates must be dome using a stable WiFi network using a dedicated WiFi network and MODEM/iFi box setup, like that found in a Home or commercial business setting.

Apple DOES NOT ALLOW any major upgrades or updates over a cellular data connection.

Sorry.