If you're using Sound Forge to create your tracks, just follow the directions below to export them as 320 kbps MP3 files.

When you're done creating your file, click the drop-down arrow next to Save in the top left corner. When you do that, a menu will appear with all of the file types you can export your track as. Here, click MP3. 

When you do that, a Save As window will appear. In that window, click the Format Settings button at the bottom. When you do that, an additional window will appear. In that new window, select 320 kBit/s then click OK.

After clicking OK, that window will disappear. Back in the Save As window, click Open to export your file. Once it's done exporting to your device, you'll be all set to upload your track to Digital DJ Pool :)