That's easy...
If you mean in the iSiloX definition...
Open your .ixl file in iSiloX.
Double click on the row that is the document you want to change, and pick the destination tab. You just change the text for document title and you're all set.
If you mean in the converted file, I believe you just change the filename.
Once installed on a Pocket PC, get into the iSilo app. Then from the document list, you can tap and hold on the document name and choose rename.
Nice program / easy answer!! Hope that helps