The "Share" feature in webclient only works with Images, but if you're sharing data with a Group of users in OMERO then you can set the Permissions of the Group to allow this.
And Admin can set the group permissions to "Read-Only" allowing other group members to read your data, "Read-Annotate" or "Read-Write".
More details are at http://help.openmicroscopy.org/sharing-data.html
I'm afraid you can't Delete a user, only disable the user so they can't log in.
As an admin you can also access the user's data and delete it to free up space.