Fizicx

I'm new to djing and im heading towards mixing with cd's. so iv'e heard when you dj at a gig you shouldn't mix with any tracks that doesnt have a bit rate of 320kbps because the sound quality isn't that great. i was wondering, when i buy cd's and upload them onto the computer the bit rate is 256kpbs (VBR). How can i use cd's but have a bit rate of 320kpbs? can anybody drop some knowledge on me? much appreciated.