sentimental cherry tree

I have a bit of a problem. Some years ago I inherited my late grandad's (edible)cherry tree. I didn't realise at the time (because it came to me already lifted wrapped in hessian) it had been grown against a horizontal trellis! I just thought it was growing odd (I was just starting to garden and was young!) so in the ground it went.
It has always fruited quite well, that is, until the last couple of years. The trained branches are huge now and point out rather than up and out. Also much of the foliage is grouped on the end of branches with lots of bare wood extending into the trees middle:cnfs:
I hope this doesn't mean my grandad's tree is past it. Could someone advise me how to prune back the tree so as to regain some shape and future productivity.

I always feed the tree well with good quality fertilizer early spring, during the fruiting period and a good feed late Autumn--is this the right way?
If photo's would help any, let me know and I'll put a few up on image shack of it.

Thanks a bunch in advance for any .

 

Hi deets,

Aye, pop some pics up if you can - it would help us see how the tree is developing. Cheers.