Audit of Asp.net & MS Sql Based Web applications

We have web applications which is developed in asp.net(vb.net) & MS sql , we have almost 300 plus forms and reports , we are facing slowness issues on data retrieval or stucked in long period reports , overall all system performace is slow , its user complain , need to identify primary reason of slowness and need to resolve slowness issues permanently
all work on strickly confidential mode