how to increase brush size in illustrator cs5

With the warp tool selected, in your workspace, hold a mouse-click whilst pressing alt. You can then drag the mouse towards the middle or outwards to make the warp tool smaller or bigger. If you also hold shift whilst doing this you will maintain the aspect ratio of the warp tool. 

Answered Aug, 02 2010

Double click on the Crystallize Tool button to open the dialog box.
enter the size you want, click OK to quit.
hope that is helpful
Answered Dec, 08 2010

1. Draw a shape of which you want to create a pattern of. For example, we created this leaf.
2. Select the shape and drag it onto the Brushes Panel. If you do not have your Brushes Panel open, go to Window > Brushes. The ‘New Brush’ dialog box will be prompted
3. Choose ‘Pattern Brush’ option and click OK. The ‘Pattern Brush Options’ dialog box will be prompted next.
Adjust the size of the brush using the Scale handler and explore other options. Click OK to apply settings. The brush will now be visible in the Brushes panel as shown below. Now you can apply the brush to any path. For example, I create this path and applied the brush from the panel;
All seems well until now. Lets try applying this border to a rectangle. Draw a rectangle and then choose this brush from the Brushes Panel.
Oh dear god! This isn’t what I was looking for. First of all the size of the leaves is way too big for the rectangle, which we can easily adjust using the ‘Scale option’ in the ‘Pattern Brush Options’ window. The second and most important thing is that the corners are all empty. And why is that? The answer is simple. This is because we haven’t set any pattern for the corners. Look at the brushes panel.
We have opened a border brush from the Brushes Library (Open Brush Library > Borders > Borders_Novelty > Coffee Cups). If you observe carefully, there are sections in which the brush is broken into. The first section shows how the brush would be applied to the outer corners, middle sections show how the brush applied to a straight path and the last one shows how the brush applies to the inner corners.

In case of our brush, the first and the last sections are empty. In other words, we haven’t defined the designs that should be displayed around the corners. To make this more clear, double click on the border ‘Coffee Cups’.
What I mentioned earlier is depicted through pictures in this window. There are different designs based on the different corners that a border can take.

All we need to do now is define how our brush (‘Leaf’) would look around the corners. To do that, define the brush on the art board. I will give an angle of 25 to the original leaf we created.
Now select this new leaf and ALT + drag + drop onto the first section of our brush in the Brushes Panel. The Pattern Brush Options window will be prompted once again, but this time you will notice the new leaf as a corner design. Answered Jun, 06 2011