If the application shows as 'Custom' in the application listing then contact the developer via his own website, request the new package, and update by manually uploading.
If the applications shows as 'Marketplace' in the application listing (which it may do, if you matched it up during your 4.x to 4.5.x upgrade) but you didn't buy the app via the Marketplace then approach IPS Support, via the Client Area, for assistance with changing it to a 'Custom' entry in the listing, and then contact the developer via his own website, request the new package, and update by manually uploading.