In the left sidebar navigation, click on your game you would like to change/remove your Game Account in.
When you have entered the game page, you will see your Game Account appear below the game title.
By hovering over your Game Account and clicking on the settings icon, you will be able to edit your Game Account.
Please note: If you have any kind of ongoing activity, even if you are only in the team finder and no tournament or ladder, you cannot remove your game account.
Double check that you don't have any ongoing activities before trying to remove a game account.
Counter-Strike: Global Offensive
If you'd like to change your Steam account for CS:GO, simply click on Counter-Strike: Global Offensive in your left navigation bar,
Then hover above your Game Account and click on the settings button.
Click on REMOVE and your current account will be disconnected from Challengermode. After that you can add another account.
Note that it's not possible to add a Steam account that has been previously connected to another Challengermode user.
League of Legends
If you want to change or add another League of Legends Summoner, click on League of Legends in your left navigation bar.
You will then enter the League of Legends game page.
Hover over your Game Account and click on the Settings icon.
You can click REMOVE to disconnect your Summoner from a specific region, and you can also add a new Summoner (when you haven't added a Summoner from every region.)
Note that you can only have ONE Summoner from each League of Legends region. Currently, EUW or EUNE are supported.
The primary Summoner is chosen automatically based on which has the highest rank or level.