Upgrade ios6 to 13

Hello ~ You can update to iOS 12.5.7 but no further. Click on the links below….

Update your iPhone or iPad - Apple Support

If your iPhone or iPad won't update - Apple Support

If you need a higher version of iOS you will need a newer iPhone. Click below to shop for a new device…

iPhone - Apple Official Site

If you purchase a second hand device please take a moment to read these helpful links by clicking on below to make an informed decision…

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Also:

The All Too Common SAD Reality of Buying a Used iPad/iPhone

~Katana-San~

If you are referring to iOS 6, as stated in the title

If your iPhone cannot update beyond iOS 6.1.6, then have an iPhone 3GS.

iPhone 3GS is almost 14 years old and was discontinued in September 2012. Major software update support ended on September 2013, although Apple continued to receive security updates until 2014, with the latest being iOS 6.1.6.

Your iPhone cannot update to iOS 7 or later due to your internal hardware being too old to support it. (Your iPhone 3GS has only 256MB RAM and iOS 7 requires 512MB RAM)

App developers dropped support for 32-bit devices and those preceding iOS 11/12/13 in the apps, making your iPhone limited in usability.

If you are referring to iPhone 6, as stated in the tags

Then your iPhone cannot update to iOS 13 or later due to your internal hardware being too old to support it - iOS 13 requires 2GB RAM or more and your iPhone only has 1GB RAM.

Apple ended major software update support for your iPhone in September 2019 - although it continues to receive security updates - with the most recent being iOS 12.5.7, released January 2023.

Many app developers have dropped support for iOS 12.x in its apps, often because the APIs in its apps have updated to the most recent version, making this iOS version not compatible.

The iPhone 6 is over 8 years old.

What to consider

iPhone 8 and later models are capable of supporting iOS 16.

You may consider buying a new iPhone. Even the entry-level iPhone SE can run the latest iOS version, iOS 16.3.1.

Here is a list of unsupported iPhones with max iOS supported:

Model            Architecture  Introduced       Max supported iOS
iPhone (1st)     32-bit        June 2007        iOS 3.1.3
iPhone 3G        32-bit        July 2008        iOS 4.2.1
iPhone 3GS       32-bit        June 2009        iOS 6.1.6 <- Likely your iPhone model
iPhone 4         32-bit        June 2010        iOS 7.1.2
iPhone 4S        32-bit        October 2011     iOS 9.3.6
iPhone 5         32-bit        September 2012   iOS 10.3.4
iPhone 5C        32-bit        September 2013   iOS 10.3.3
iPhone 5S        64-bit        September 2013   iOS 12.5.7
iPhone 6         64-bit        September 2014   iOS 12.5.7 <- Likely your iPhone model
iPhone 6 Plus    64-bit        September 2014   iOS 12.5.7
iPhone 6S        64-bit        September 2015   iOS 15.7.3
iPhone 6S Plus   64-bit        September 2015   iOS 15.7.3
iPhone SE (1st)  64-bit        March 2016       iOS 15.7.3
iPhone 7         64-bit        September 2016   iOS 15.7.3
iPhone 7 Plus    64-bit        September 2016   iOS 15.7.3

Or be on the look-out for a properly prepared iPhone 8 -or newer- model

that could be able to use your SIM card; between that, and a new battery?

..There are additional steps to consider, as well..

To research the field, for a pre-owned model (a cellular provider

in your area, may have some unlocked older iPhones for sale)

some independent authorized cellular providers could do that.

Identify your iPhone model - Apple Support

//support.apple.com/en-us/HT201296

iOS version history - Wikipedia

https://en.wikipedia.org/wiki/IOS_version_history

List Of All Apple iOS ~ Version History (Current iOS Version 2023) - GkGigs

https://www.gkgigs.com/list-apple-ios-version-history/

The cross section of hardware vs software model year iPhone

and associated iOS, may help you, should opportunity knock.

Support pages such as this could be useful to check n' see

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

~ if you buy a used suitable model; to sort wheat/chaff.

[A re-seller should prepare their product so you don't see an

"activation lock" as could happen otherwise, if unprepared.]

This may happen with any previously-owned Apple product.

To avoid this, read and research carefully..

• Activation Lock for iPhone, iPad, and iPod touch - Apple Support

//support.apple.com/en-us/HT201365

However if you know a local AASP (authorized apple service)

who can repair Apple products, ask about repaired iPhones.

{I received second-hand iPhone 8 from my brother, who got

a newer model from GCI cellular provider in Anchorage. He

gave me that one; though it lacks a SIM card & new battery.}

..I'm still using first edition iPhone SE, runs iOS 15.7.3 tops;

but the newer model, an iPhone 8, runs current iOS 16.3..

In order to update an iOS for those newer apps to run

you'd certainly need a newer iPhone model hardware.

iOS 12.x is tops for an iPhone 6.