thanks I will try that out. :) 

Now the clicks make it switch too fast

maybe just use mouseReleased instead of mousePressed()

Also I get an ArrayIndexOutOfBoundsException:14 error.

I assume you got 13 images.
When you increase the index you have to check if it's bigger than the array size.
If so, set index to zero or set it to array size-1.
(when you decrease the index you need to check for zero too)

Greetings, Chrisir   

implement a mousePressed() event function to increase that index or go back to 0.

That was my 3rd tip! 

Here're 2 algorithm choices to guarantee index won't extrapolate its limit:

void MousePressed() {
  if (++idx == name.length)  idx = 0;
}

void MousePressed() {
  idx = (idx + 1) % name.length;
}

Wow that is way more simple, than the way I had coded it. Here is what I had. 

Here's an even shorter version. Just rename 1st "thor.gif" to "thor1.gif" for it to work though! 
[EDIT] -> newer version: left-click to go back or right-click to go forward! 

final static byte IMAGES = 14;
final static PImage[] images = new PImage[IMAGES];

final static String NAME = "thor", EXT = ".gif";

byte idx;

void setup() {
  size(600, 400);
  noLoop();

  for ( int i = 0; i != IMAGES; 
  ( images[i] = loadImage(NAME + ++i + EXT) )
  .resize(width, height) );
}

void draw() {
  background(images[idx]);
}

void MousePressed() {
  redraw();

  if (mouseButton == LEFT && --idx == -1)  idx = IMAGES - 1;
  else if (++idx == IMAGES)  idx = 0;
}

Thanks, I had to make some changes to your code. I should of said that I am learning to code for Android. Your code crashed. I believe it was too intensive on memory (not really sure just crashed). Other than that I really appreciate your help. time to move onto my next little project to learn.