You have to unmount/remove the card, before you can upload a compact flash image to your card.
Downloads as well as uploads are limited to a maximum size of 2 GB each. To upload a complete image, you must split the image in to parts of 2 GB each. When downloading an image, the box will deliver a 2GB part for each download. You need to select the appropriate image part numbers in the Select the current image part for upload/download dropdown before you up/download the respective part.
Select an uncompressed image file part and upload it to your compact flash or SSD card.
Warning: this will delete all partitions and files, which are currently present on your card!
Downloads the currently selected part.
To create an own image from a CF card under windows, you can use the Securepoint Imaging Tool.
If you want to upload such an image, you have to split it into 2.147.483.136 bytes sized parts. There are enough free tools available for this job.