I have downloaded the update but i am unable to install it. It’s showing some errors

You need to be on a WiFi connection to install the iOS update.

Also

Make sure you:

• Have your battery charged at least 50%. Better yet, keep it plugged in during the update.

• Are not using a VPN connection.

• Do not have power save mode turned on.

• Do not have a beta version installed.

• You have at least 6 gigs of storage available.

You can also check out this article for help -

If your iPhone, iPad or iPod touch won’t update

https://support.apple.com/en-gb/HT201435

What version of iOS are you currently on? Go to Settings > General > About and it will tell you what version you are on.