To get started, simply go to the Clients tab → Agents
Look up the client you'll be modifying - once you have located them, click on Edit
However over their profile photo and you should see this
For the Agent Logo, navigate over to the Display logo page and you should see that here:
Hover over to the photo and you'll see this:
Note: You can add a logo to the Company record. All agents assigned to this company will automatically use this logo. An agent logo will override a company logo