Can I use this one for my iPhone 6plus?

What might “this” be that you are looking to use, here? iOS 14? No. You will not be able to update an iPhone 6 Plus past iOS 12. There are no hardware upgrades available. The only option for running current iOS is a newer or new iPhone; iPhone 6s or later. (iPhone 6s has twice the memory of an iPhone 6, among other differences.)

sec49 wrote:

Okay what kind of iOS can I upgrade my iPhone 6plus to?

You’re almost certainly already running it. Currently iOS 12.5.4, as mentioned above.

Any recent iPhone will be far more capable than an iPhone 6 Plus, as well.

iOS 12.5.4 is the highest version an iPhone 6 Plus can run.