Can I delete my picture library from the hard drive once it is backed up ?

Hi, my mac book is so full I am getting the beach ball symbol all the time in i photo.
I have plugged in a seagate external drive and it has done the time machine upload. I have also copied the picture library onto the external drive to be sure the images are backed up.
When I unplug the external hard drive and try and delete from events it is much to slow and the beach ball soon appears.
I have noticed when I access the picture library from the hard drive icon there is an option to press a delete button to empty the pictures of the hard drive?

Will this work ?

Thanks in advance

If you don't fully understand what it is you're going to do and the possible consequences of doing it, I'd say you are begging for disaster.

Under NO circumstances should you be messing around with iPhoto's actual photo library file. If you want to back up your iPhoto library to an external drive, copy the ENTIRE iPhoto Library file to the external drive, then fire up iPhoto with the option key held down and redirect the program to use the external drive for the default library location.

THEN you can safely remove the original photo library on your boot drive.

thanks, I will try that,