Well, in theory you can just right click in CM and select 'upload'...
But in practice, you want to export from CM to a .cdp, then go to 'Planet Auran' from www.auran.com, select 'Your Content' under the Trainz Menu on the left of the page, click 'upload content', then 'standard upload', click 'choose file' and select the file on your PC that you exported from CM, then click 'OK' then click 'Submit' and that should be it.
Then wait and hope the DLS takes it (if you get the 'unable to commit due to file access' error, or something like that, just resubmit it)
A .cdp file (content dispatcher package?) is what all Trainz content is generally saved as. It can contain one asset or many.
The way to get the thumbnail in is:
-Find your route in CMP
-Right click and select 'open in explorer'
-Put your thumbnail in the folder that appears (240x180 jpeg file)
-open the file config.txt (a notepad file)
-add this text into the file at the end:
-save the file and close the folder
-select the route in CMP again, and press ctrl+M (to commit)
You can then use the built-in up-loader in CMP, or right click and use the save to .cdp option, and then upload the file through the 'your content' tab in Planet Auran.