Question marked as
1.
You need about 7 GB device storage, see this Apple articles below:
If you need more space for an update on your iPhone, iPad, or iPod touch
https://support.apple.com/en-us/HT203097
How to check the storage on your iPhone, iPad and iPod touch
https://support.apple.com/en-gb/HT201656
Clear Other storage on your iPhone or iPad
https://support.apple.com/en-us/HT211686
What's the difference between device storage and iCloud storage?
https://support.apple.com/en-us/HT206504
2.
Try to optimize the range of the mobile network, see this Apple article: If you see No Service or Searching on your iPhone or iPad
https://support.apple.com/en-us/HT201415
3.
Check also the Wi-Fi network, see this Apple article: If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network
https://support.apple.com/en-us/HT204051
4.
See also the following Apple articles:
Update your iPhone, iPad, or iPod touch
https://support.apple.com/en-in/HT204204
If your iPhone, iPad or iPod touch won’t update
https://support.apple.com/en-us/HT201435
5.
If they are On, turn Off Hotspot & VPN.