Upload my skin to Minecraft: Java Edition

Before modifying the skin, make sure you have already paid Minecraft Java Edition (demo versions won't work) and the game is not running while changing your skin. There're two ways you can change your skin:

Method 1: Upload in Minecraft.net

 ​ 

Go to https://www.minecraft.net/en-us/login and log in your Microsoft account.

Then you will be redirected to the following page, click Change Skin under the "MINECREAFT: JAVA EDITION".

Choose the model of your skin, and scroll down the page.

Click Select File, and select your new skin file on your computer.

Finally, click the "Upload" button, your new skin is now ready!

Method 2: Upload via launcher

 ​ 

Open the Minecraft Launcher, once the launcher opens, don't click the play button as usual, instead, click Skins tab.

Click the New Skin button.

Write down the name, select the model type and upload your skin file. click on the Browse button to select your PNG skin file.

Finally, click Save & Use to save the changes.

Now launch the game, and you shuold be able to see your new skin.