Can I update my iPhone 6s to iOS 14?

iOS 14 isn't available to the public currently, it is only for registered developers. A beta option may be offered for the general public sometime next month in July, and the official release will be later this year in the autumn.

In the meantime, you can update to the most current version of iOS.

Go into Settings > General > Software Update --if any updates are available, they will be presented there.

Follow the instructions here: https://support.apple.com/en-us/HT204204

In the future, you can go the apple website to check for public beta: https://beta.apple.com

Right now? no, only developer betas are available at this time.

Will iPhone 6🅂 support iOS 14? Yes, you can install it when it's released to the public, or via public betas in July.