Convert Date/Time to Date

I have a query which runs and I would like to return records where the date is greater than or equal to a particular date. The column I'm querying against is datetime format.

SELECT COUNT(RSO_ParentID), AssignedDateTime
FROM Task
WHERE OwnerTeam='2nd Line Support' AND AssignedDateTime>='2015-09-01 00:00:00.000'
GROUP BY AssignedDateTime

Is there a way of having filtering on the date part of AssignedDateTime, and searching relative to the current date (i.e. search for the previous 7 days)?

Thanks, Matt