It looks like you need to navigate to the folder where you want to upload the file. Then press the upload button which is the icon that looks like a box with an arrow in it pointing upwards. Select the file you want to upload. Press open. Then you'll get the spinning circle as the app uploads the file. The app will tell you when it's done uploading and you confirm by pressing ok.

The upload button is grayed out when you're in the filter, so you will need to manually navigate to the folder you want to upload to (on mine i select the fourth option down on the app's home screen).

I tried this with two photos and it worked fine. I don't know about other files right now (I don't have any music or video on my phone since i just re-flashed it today).