You can prune them but they are just going to grow back. And the laterals aren't going to magically start growing where you want them to. Instead I'd suggest training them to the open vase shape you want. And tip them if they get too long and floppy.

My trees are small so I don't go for the open vase shape. Mine are more a small bush. I do tip the branches when they reach the max height I'm wanting.

Thanks fruitnut. Any suggestions on how to train them?

Also, I'm not familiar with the term "tip them". What does that mean?

Tipping just means to pinch out the tip. I train using strings tried off to a stake or weight on the ground. Don't strangle the branch. Rather loop the string over the branch and pull it where you want it positioned.

Select just 3 or 4 of all the branches and leaders, and train them down so they spread out, and prune off all the others. If you like where the lower ones are already, just prune out all the tall spindly ones. Personally I'd rather get rid of those spindly ones and keep the ones that have the most leaves on them. Then 3 or 4 times per year, continue to prune out any new leaders or branches that shade the center of the tree. Search YouTube for Dave Wilson Nurseries and you'll find dozens of videos that show exactly how to do this.

There's really no right or wrong way to prune. Or should I say, the right way to do it is the way YOU want it. If you want an open center, then prune to maintain an open center. Simple as that, really.

Thanks everyone for your replies.

dmtaylor - I've come to realize that "there is no right way," as you say, when it comes to gardening. It's nice, though, to hear from lots of different people and then make your own decision.