Google is an amazing thing. A simple search reveals that you are due to dock at S167 at 10am on 30August. This is Stadsgarden - most cruise lines lay on a shuttle into town or it is a simple 30 min walk.
We returned on the 9th July from this cruise and the Crown anchored off Nynashamn (but we don't know why) so we had to come ashore on the tenders, then use a shuttle bus to get to Stockholm, which was quite expensive and took at least 30 minutes. the old town is lovely we were in Stockholm on the 1st July and it was about 25 degrees.