If you make changes to paper after initial conference submission, should you present updated version at conference? I am a PhD student in computer science and have submitted a paper to a conference which details my proposed architecture. However in the month or so since this paper has been submitted my architecture has undergone changes (relatively major), how is this normally dealt with?

If the paper is accepted do I present the work as it was at the time of submission or do I openly state that changes have been made and present the updated version of the architecture?
I believe you should do what is better to the audience. 

In some disciplines/communities it is strongly assumed that conference participants read the abstracts/papers before the presentation, and expect the discussion to follow precisely the material that is published. In this case, of course, you could only comment briefly on the recent changes you've made.

In other fields (such as mine), the abstracts are used only as a means to (roughly) describe the topic of the presentation. It is quite normal to extend the actual talk beyond the scope of the abstract, or reduce the role of some pieces of research advertised in the abstract. In this case, I'd advise you to make a talk that is simply interesting for you and the audience. It can probably include both the original design and your contribution to its recent development. Make sure people in the room understand why  the changes were needed, how you have worked them out, and what is the benefits of your new architecture.