Getting Started: A New User's Experience on Slack

Hi. This is my first time using Slack, so I hope I'm doing this right!!! 😬 I'm using Relume for the first time and so far it looks good, but I'd like to know how to customise the images in the Style Guide. Is there any way of adding my own and choosing where each one goes? I'm just thinking if I am going to pitch concepts to clients then it would be best to use relevant images to their site, not random stock ones