You can possibly convert the files to lossless, but the information contained in your converted file remains the same as that in the MP3 which is not a good thing.
You can convert from MP3 to AAC (which is really MP4) and they will sound better. I'm not sure that you can convert the DRM'd files though.
If you want to buy better sounding recordings there are other places on the 'net including Amazon where you can do so. In some cases (itrax.com and hdtracks.com for example) you can get original lossless and even high resolution audio recordings for a premium. Check that your player is capable of playing high resolution audio before buying.