PSQRYSRV Increase minimum and maximum

I would like to know how to determine the appropiate setting (minimum/maximum) instances for our PSQRYSRV. What are the consideration for increasing this parameters?

Below are the current settings.

[PSAPPSRV] 
Min Instances 2
Max Instances 5
Service Timeout 1200
Recycle Count 1000
Allowed Consec Service Failures 0
Max Fetch Size 20000
Auto Select Prompts 1
Tuxedo Queue Size 65535
  
[PSQCKSRV] 
Min Instances 1
Max Instances 3
Service Timeout 0
Recycle Count 0
Allowed Consec Service Failures 0
Max Fetch Size 5000
  
[PSQRYSRV] 
Min Instances 2
Max Instances 3
Service Timeout 1200
Recycle Count 0
Allowed Consec Service Failures 0
Max Fetch Size 20000
Use dirty-read 0

Server Specs:4 CPU'sTotal Physical Memory                        12,287.06 MB

Available Physical Memory                4.45 GB

Total Virtual Memory