How do i put all my photos on my computer? and then get all my photos off my phone?

Follow the Mac or PC instructions in:

Transfer photos and videos from your iPhone, iPad, or iPod touch - Apple Support

Once they are on your computer (you may even want to copy them to an external drive) then you can delete them on your iPhone.

Delete photos on your iPhone, iPad, and iPod touch - Apple Support

Take a look at Transfer photos and videos from your iPhone, iPad, or iPod touch. Keep in mind that if your computer syncs your photos to iCloud and your iPhone is set to sync with the iCloud, they'll wind up right back on your phone. ;)