What you need to do is copy out the photos onto a computer then delete the photos inside the phone. After you have done that you then copy all the photos in to the microSD card if you have enough space.
Make sure you also copy videos of course. The file location for photos usually are as follows:
Stored in phone memory: Internal Storage/DCIM/Camera
Stored in memory card: SD Card/DCIM/ Camera
You may additionally need to set the storage mode after plugging in the phone and unlocking the phone via the notification / status bar at the top drag it down and select MTP (Media Transfer Protocol). I think that is what it's called for the latest android operating system for your Samsung Galaxy S5.
TL:DR - Copy all photos from phone memory and memory card, delete photos on phone, copy them back into to memory card and you should have more space for internal storage.