Tell me any way to download latest version of iOS in iPhone 5

The latest version for the iPhone 5 is iOS 10.3.4. If you have problems with downloading or installing the update, see:

Get help with iOS updates

https://support.apple.com/en-us/HT209571

Get help with over-the-air iOS updates

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

Get help with iOS update and restore errors

https://support.apple.com/en-us/HT204770

If you are talking about iOS 11 or 12, there is no way. iPhone 5 is too old and has insufficient hardware for anything newer than iOS 10.3.x.

No. The iPhone 5 is no longer receiving iOS updates.

It can not run anything higher than 10.3.3