Lightroom 3.3 - Pana 20mm/f1,7 - Barrel distrtion correction?

Hi, I have a 20mm/1.7 pana lens and a pana G2. When reading the review of the lens on lenstip, I find that the distortion is huge. While shooting jpg, this is corrected within the camera but I am intending to only shoot raw and then postprocess the images in Adobe Lightroom 3.3. How can I correct the distortion in Lightroom? Do I have to download an plugin and how do I use it? Any tip is very welcom.

Regards, Gustav in sweden