you will need to determine what the radius of the sprinkler head needs to be to water the area properly and what the spray pattern each spray head you require is.
Then you need to measure how far it is from head to head on what you have now.
Then look at the sprays available and determine which spray head is best for your application.
Pay attention to the PSI that you have and try and determine what the psi will be at the spray head. Some heads work better at X psi than they do at x+ or x- psi.
There are spray bodies available with built in pressure regulators that can help with too high psi if that's the case
Recommend to read the irrigation tutorial in order to get a better grip on the situation.
http://www.irrigationtutorials.com/sprinkler00.htm
you will probably have to copy and past the link into your browser.