Can I upgrade my iPhone 6 for a new model or update its software?

hello every one.

11 years ago I bought 2 Iphone 6, 128 gb of memory... a wonderful machine... My experience an my wife experience has been incredible, a very beautiful cellphone, very strong, very good as cell phone !!

Recently some very importants apps has warning me that they wont work with my iphone any more due to the old version of my software.

Does any one nows if i can change this model for a new one for free?Does Apple change this old versions?...or any kind of bussiness with my old Iphones 6 ?

May i update my old IOS version ???.....

Any advice will be apreciated....

Regards.

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