You should be able to do it while logged into the site.
Go into your User CP (the link up there on the left).
At the top of your CP you should see "subscribed threads".
In the bottom right margin of that you see "View all subscribed threads".
Once there you can select threads using the checkbox on the right... or you can use the checkbox in the header to select all threads.
Then in the bottom of the list there is a little drop down labeled "Selected threads." You can change the notification type to None, Instant, Daily, Weekly. Note, each thread can have a separate notification type.
Also, as Tom mentioned you can change your default in your settings to the same options. However the default only applies new subscriptions.
Last edited by pilotbob; 11-10-2012 at 02:23 PM.