How to delete or move submitted assignments in Moodle 2.4.3

Hi.

I think answer is no, but i'm asking anyway. Is there anyway to delete old submitted assignments from course as Moodle administrator. We have few very large courses because of those submitted assignments and there are active users all the time so i cannot backup the course and restore it without user data.

Second question is can i somehow move or copy those active users with their user data to different course. I mean that if i backup the course and restore it without user data and then want to get active users with user data to use restored course. This way unactive users with their userdata will be removed. 

Thanks in advance

~ Jukka ~