If you have access to the source code for both sketches, you could just merge them in the code directly, and decide which one is running by keeping track of some state variable, like so:

1. int state;
   
   void setup(){
     size(300,300);
     state = 0;
   }
   
   void draw(){
    
     if(state==0){
       background(0);
       state = 1;
     }
    
     if(state == 1){
       stroke(128 + random(128), 128 + random(128), 128 + random(128));
       noFill();
       line( random(width), random(height), random(width), random(height) );
     }
    
     if(state==2){
       fill(128 + random(128), 128 + random(128), 128 + random(128));
       noStroke();
       ellipseMode(CENTER);
       ellipse(random(width), random(height), 20, 20);
     }
    
   }
   
   void mouseClicked(){
     if(state==0){ return; }
     if(state==1){ state=2; return; }
     if(state==2){ state=1; return; }
   }
   
   void keyPressed(){
     if(state==0){ return; }
     if(state==1){ state=0; return; }
     if(state==2){ background(255,0,0); return; }
   }
   

You can check out the napplet library:

Thanks tfguy44 and jack for your reply.

I believe NApplet is  what I am looking for.But I also want to control the creation and deletion of the NApplet .
That is I have certain buttons on the base sketch and on click of any of the button previous NApplet should be destroyed and new sketch should open up.
I know how to create NApplet but doesn't have any idea about how to kill them.

Please help.