She will eat most things - tends to have dry food in the morning and a couple of cans of supermarket own food in the evening. She's well and enjoys her walks; doesn't do much - just acts like a greyhound 
Now she's getting older, and I have a little more money available, I was thinking of changing her diet, perhaps to one of those foods that you give less in quanity but more in quality. Haven't a clue which to choose - can you advise?