here are the steps you'll need to take to log out of Xbox Live in Minecraft for Windows 10. It involves modifying an options text file:

• Press Windows Key+R to open the Run dialog, then copy and paste the below address and press Enter:

%localappdata%\packages\microsoft.minecraftuwp_8WEKYB3D8BBWE\localstate\games\com.mojang\minecraftpe

• Open the options.txt file and change these two variables to the below values:
  game_haseverloggedintoxbl: 0
  game_haschosennottosignintoxbl: 1

Save the file, then try running Minecraft again. You should be logged out now.