You can change your name in the Java Edition for free as many times as you want, but you must wait 30 days between name changes. For the Bedrock edition, it uses a Microsoft Account.

Select “Profile Name” Change to the desired name and save This name change doesn’t effect the Gamertag found on the Xbox account, and will only be shown when playing Java edition.

How do I find my Minecraft username? On the change name screen, you can see your previous name located right after the field “Current Java/Bedrock Profile Name”.