Removing the toner cartridge:

https://infoserve.lexmark.com/ids/idv/video.aspx?category=Multifunction+Products&productCode=Lexmark_MX511&topic=v27304658&vId=MSX31x_41x_51x_61x%2fmfp_supplies_toner_remove&ar=4%3a3&ap=1&l1=3&l2=1&sh=937&sw=1920&loc=en_CA

Replacing the toner cartridge:
https://infoserve.lexmark.com/ids/idv/video.aspx?category=Multifunction+Products&productCode=Lexmark_MX511&topic=v27304658&vId=MSX31x_41x_51x_61x%2fmfp_supplies_toner_insert&ar=4%3a3&ap=1&l1=3&l2=1&sh=937&sw=1920&loc=en_CA