How does one adjust the number of snapshots for hammer to keep?

In the man page it says:
HAMMER version 3+
The configuration file is saved in file system meta-data
....
The format of the configuration file is:
 snapshots  <period> <retention-time> [any]

What ist he name of the configuration file?
.snapshots.period ? That files does not seem human readable/editable.

Also the man page has: "see hammer config."
Is that another section in the man page or another man page? Tried man 5 
hammer and searchign for "hammer config" in the main man page.

To delete a snapshot do I just delete the link and prune?
Example
I deleted a few links from /var/hammer/root and then did
hammer prune /var/hammer/root

Got 
TID 0000000106239300 - 00000001062e2490
TID 0000000104c82520 - 0000000106239300
TID 0000000104a207b0 - 0000000104c82520
TID 00000001043d8dd0 - 0000000104a207b0
TID 00000001040614a0 - 00000001043d8dd0
TID 0000000103616010 - 00000001040614a0
TID 00000001028fb580 - 0000000103616010
TID 00000001028d5dc0 - 00000001028fb580
TID 00000001020f72d0 - 00000001028d5dc0
TID 0000000000000001 - 00000001020f72d0
Prune //: 10 snapshots
Prune //: objspace 8000000000000000:0000 7fffffffffffffff:ffff pfs_id 0
Prune //: prune_min is 0d/00:00:00
Prune // failed: Input/output error <---- Error?
Pruned 0/0 records (0 directory entries) and 0 bytes


Don't see any difference in df. When/how is the space regained?
Had a lot of extra data so now that I cleaned things up I want to delete the 
snapshots with the extra data to get the space back.