The only way of adding historic seasons details would be to up-load all the information a season at a time i.e. adding all the fixtures, results, players stats etc. Then you would need to archive this information and reset the site and then repeat the process for each season.
However, please ensure that you have no current "season data" on the site that has not been archived first. When you reset the season this removes all this data.
An easier option would be to add all this information to a document and upload it to the "documents" area.