Hey Andrew,
Anyway, can wyBuild be integrated into installshield or my app to automatically update my app
Yes, this is what wyBuild was designed for. A good place to start is the intro video or the step-by-step walkthrough.
or would wyBuild replace installshield all together?
We're adding the ability to make installers in wyBuild 2.7. In the meantime you should use Inno Setup, NSIS, or WiX. Installshield is a fairly mediocre product especially when compared to those 3 great open source products I just listed.