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

When you're done creating your track, click File in the top left corner, then click Export. From there, select Multitrack Mixdown > Entire Session. 

When you do that, an Export Multitrack Mixdown window will appear. In that window, head to the Format drop-down menu and select MP3. In that same window, you'll see a section called Format Settings, which is where you'll see your track's bitrate. If that section does not have "320 kbps" in it, click the Change button next to that section. From there, you'll be able to set it to 320 kbps.

Once that's all done, just click OK and your track will be exported and ready to upload to Digital DJ Pool :)