How can I update my browser Safari to use my credit card?

To upgrade Safari from Safari 15.6.1 to a later version you would need to upgrade your Mac from macOS 10.15.7 to a later version.

The model year of a MacBook Air is available at Apple menu > About This Mac.

A mid 2012 MacBook Air can be upgraded to Catalina 10.15.7 but no later. See: How to download and install macOS - Apple Support

A mid 2013 and early 2014 MacBook Air can be upgraded to the latest version of Big Sur macOS 11 but no later. See: How to download and install macOS - Apple Support

An early 2015 and a 2017 MacBook Air can be upgraded to the latest version of Monterey macOS 12 but no later. See: How to download and install macOS - Apple Support

A 2018 or later MacBook Air can be upgraded to the current version of Sonoma macOS 14. See: How to upgrade to macOS Sonoma - Apple Support

If you can’t or don’t want to upgrade, you may want to use a 3rd party internet browser that supports running their current version on your Mac. One option is Chrome: https://www.google.com/chrome/

Marie R wrote:

One of my credit card accounts tells me I have to update my browser.

JP Morgan Chase?

This is their problem to fix. They need to stop using the outdated and privacy-intrusive "user agent" query. Unfortunately, that leaves you out in the cold until they realize the error of their ways and correct it.

The workaround for end users who are unable to update their Macs to a newer macOS version is to use a different browser.

Consider Brave:

https://brave.com/

Firefox is a distant second choice:

https://www.mozilla.org/en-US/firefox/new/

The bottom line is that there is nothing wrong with your Mac's version of Safari, but that bank is using an outdated and ill-conceived method of determining browser requirements. If you are so motivated direct their attention to the WWW publication User-Agent Client Hints (courtesy VikingOSX).

In-depth background discussion here: chase wants me to update safari to 16, should I do that? - Apple Community