We often hear from customers who are changing a Genuine Brother or Compatible Brother toner for the first time the the item removed from the printer is larger that the new toner they have received.
This is because the item you remove from your printer is the drum and toner unit combined. Your toner sits inside the drum and needs to be removed and replaced with the new cartridge we have delivered to you.
On the nearside of the drum unit, usually the left or right hand corner is a blue or green lever or button. Press this and the toner will be released, the movement can be quite subtle, like a little pop. Remove your old toner from the drum, take your new toner, ensuring the clip protecting the roller has been removed and insert this into the drum. Return this combined unit into the printer again.
Here is a sample label that may help you.