Reformatting Iphoto and Photos

I noticed my iphotos and photos is killing the space on my macbook pro (300+GB in each app).

Is your Photos Library an migrated iPhoto Library? If you migrated the iPhoto Library to Photos, both applications are sharing the storage for the original master files and the previews by using hard links to the photos. If both libraries are showing a size of 300GB, they will together only use about 400GB, as long as you do not import new photos to Photos that are not in the iPhoto library. So you may not save much storage by deleting the libraries and starting over. See these documents:

• Photos saves disk space by sharing images with your iPhoto or Aperture libraries - Apple Support
• and Six Colors: The (hard) link between Photos and iPhoto

and now i want to reset my iphoto and photos back to zero like as if it was new. Is there any easy way to do this?

You can create a new, empty Photos Library by launching Photos while holding down the options key. This will bring up the library chooser panel and you can select to create a new library. Then make a backup copy of your previous Photos library and delete the previous Photos library from your Pictures folder. You can create a new iPhoto Library the same way by launching iPhoto while holding down the options key.