To remove the Wurst Client logo, you can change its visibility in the settings. If you're using ClickGUI, you can open the "UI Settings" window, click on the arrow next to "WurstLogo", and set the visibility to "Only when outdated."
If you're using the Navigator GUI, simply search for "WurstLogo," and you'll find the same visibility settings. Set it to "Only when outdated."
Hope this helps!