If you're using Ableton Live to create your tracks, just follow the directions below to export them as 320 kbps MP3 files.
Once you're done creating your track, make sure that you have it all highlighted in Ableton. After that, click File > Export Audio/Video. When you do that, an Export Audio/Video window will pop up. In that window, you'll see an MP3 section. In that section, make sure the toggle next to "Encode MP3 (CBR 320)" is on.
Once that's set, just click Export at the bottom of the window. When your file is done exporting, you'll be all set to upload it to Digital DJ Pool :)