You can also do this at the CLI of the DFM server.
# dfm perf data list (see what the current retention settins are)
# dfm perf data modify help
NAME
modify -- Modify the interval and collection details for a counter group
SYNOPSIS
dfm perf data modify [ -f ] -G <counter-group-name> [ -o <host-name-or-id> ]
[ -s <sample-rate> ] [ -r <retention-period> ]
DESCRIPTION
Modify the interval and retention details for a counter group.
Specify a positive number, optionally followed by a time period
suffix to indicate seconds, minutes, hours, days, or weeks.
The default time period suffix is seconds.
'host-name-or-id' is mandatory for default counter groups.
Use -f option to force the change of sample rate and
retention period when the number of records for
the view decreases.