Anyone can rename the channels they belong to, unless the System Admin has restricted the permissions to do so using advanced permissions.
In the Desktop App, select the channel name at the top of the center pane to access the drop-down menu, then select Rename Channel. You’ll be prompted for two values:
Channel display name: This appears in the Mattermost user interface.
Channel handle: This is part of the channel URL. You can also change the channel handle when renaming a channel, but changing channel handles may break existing links.
For example, for the following channel,
https://community.mattermost.com/core/channels/ux-design, The channel display name would be
UX Design, and the channel handle would be