Please help me convert mp3 to 320kbps and 44.1khz
File → Export
Format = MP3
Sample Rate = 44100
Bit Rate Mode = Constant
Quality = 320kbps
Or, if you aren’t editing then audio you can use a converter program like Kabuu Audio Converter (free). It’s easier to use. Once you’ve set up your output location and desired format, it’s just drag, drop, and click, and you can batch-convert multiple files.
NOTE: If you are starting with an MP3, increasing the bitrate or sample rate won’t improve the sound. It’s sort-of like copying a VHS tape to Blu-Ray and expecting Blu-Ray quality. 
In fact it will theoretically degrade, although it probably won’t sound worse. As you may know, MP3 is lossy compression. Data is thrown-away to make a smaller file. When you open an MP3 in Audacity (or any regular audio editor) it gets decompressed. If you then re-export as MP3 you are going-through another generation of lossy compression and some “damage” accumulates.
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