Shared file has all the user created objects/bookmarks etc.
when you say - you want to reduce the size - what is it exactly you want to achieve?
If you really do not care about the user created objects or any info within the shared file, you can delete it (or replace it with a blank shared file)
May be i am asking you a dumb question
1. If you are talking about the .shared file which will be created in the distributed folder when anyone opens the app in the access point. If that is the case i would follow the instructions given by Rakesh.
2. Suppose if you wanted to share a physical QVW file without the data you can reduce the app and share it with others. Then they can reload it on their end. Then make some selections to reduce the data of the app then go to file --reduce data-- keep all possible values-- then save the document.