Not really sure what was giving me a problem changing the SMB share. I think it was a permissions issue.
Anyway changing the "Pictures" share (SMB) is very simple.
In the folder /etc/samba you will find a file called smb.conf. We need to edit this.
sudo nano /etc/samba/smb.conf
Scroll down to the end of the file and your will find a section called [Pictures]
modify it to contain your new path: path = /media/stellarmate/data/Pictures
^X Y to save the file
Now we need to restart samba:
sudo smbcontrol smbd reload-config
Now you should be able to view the Pictures folder on your Mac or PC.