The nas reorganize database command will run a vacuum against the internal databases. This will free up some of the size that is being used.
Note, this assumes that the database.db and transactionlog have empty pages to free. If however, you have tens of thousands of alarms you will not see much, if any, reduction in size.
You can reduce the number of rows in the transaction log by modifying a few settings in the nas GUI. This would be under the Setup -> Transaction Log Tab.
The settings with the most impact will be "Keep Transaction History" and "Keep transaction summary"
These refer to the NAS_TRANSACTION_LOG and NAS_TRANSACTION_SUMMARY tables that are internal to the transactionlog.db file.
They both affect the amount of time and information you are able to see in an alarms history from within Infrastructure Manager.