There is no known way to convert older Mathcad sheets into Prime format other than using the converter which needs a full installation of the current Mathcad 15.
But wheres your problem? Just download Mathcad 15 and install. Additionally to being able to convert older sheets you now have a more powerful and faster program than Prime probably ever will be.
If you have bought Prime you are entitled to use Mathcad with the very same license file.
If you are just using Prime Express you can also use Mathcad 15 for a trial period of 30 days.
If you use Prime Express and have already used up the trial period, you will need somebody doing the conversion for you.
Link to the english version of Mathcad 15 to download:
http://download.ptc.com/products/mathcad/trial/mc15/Mathcad15_EN.zip
