Cheers Djelle, I kept trying to update and it wouldn't work - never thought to check the folder on the image!

Forgot to write that u need to subscribe to ur own items to be able to update. In case u didn't know.

Thx for these pallets :)
U could have updated the original ones. I learned only recently as it is a bit convoluted. When u hit the update button; before accepting, click the folder icon (where u also put the image). There is a subfolder with the crp-file. Replace that file with the new model u have made and saved. Its found in something like: c:\Users\Djelle\AppData\Local\Colossal Order\Cities_Skylines\Addons\Assets\. And now u can Accept the upload.