Discord Server Icon Size
The server icon is the small symbol members look for when switching between Discord servers.
Picking a symbol for the server list
Think about how the icon will read beside your other servers. If two icons are blue circles, a lightning bolt on one and a moon on the other give members a second cue besides color.
On desktop or in your browser, open Server Settings → Server Profile and choose Change Server Icon. Save your changes and look for the new icon in the sidebar. To change the picture next to your own messages, use the Discord profile picture guide.
The channel-list banner is a separate image
For the image above the channel list, Discord recommends a 16:9 server banner at 960 × 540 px and says it can resize a 1920 × 1080 px upload for that slot. Discord lists a static channel-list banner as a Level 2 Server Boost perk. The invite splash belongs to the invitation screen.
