How can I update my iPhone 6

To update to the maximum of iOS 12.5.7, please see: Update your iPhone, iPad, or iPod touch - Apple Support

And: If your iPhone, iPad, or iPod touch won't update - Apple Support

If the above Apple articles do not help, please post back with relevant information. 

Princewise1515 wrote:

I want to update my iPhone 6 to iOS 13.5

Unfortunately, that is not possible.

The iPhone 6 is not compatible with iOS 13 or higher.

That model can be updated to iOS 12.5.7, no further.

I want to update my iPhone 6 to iOS 13.5

Not possible with iPhone 6 since it tops out at iOS 12.5.7.

If you need to run apps that require a higher iOS version, you are going to need a new phone.