I am trying to get my STAAD.Pro model to Tekla through ISM. How can I have the beams generated in STAAD to come into Tekla at top of steel rather than the middle of the beam ?

You will need to define appropriate offsets in your STAAD.Pro model for the members so that the physical location of the member matches with that in your actual structure. When you define a member in STAAD.Pro, by default the cg of the member is aligned with the line joining the start and the end nodes. If that is not what you want, as in your case, you need to use offsets to shift the cg with respect to that line. Subsequently when the ISM repository is created, ensure that the “Include Member Offsets” box is checked. Subsequently when you get the ISM model into Tekla, the beams should be aligned such that the top of the beam is at the TOS.