how to swtich extjs themes?

I noticed that extjs comes with 3 to 4 default themes/skins . How can I select or swtich between the themes?

I want to change the blue to select the grey themes or something else.

Thanks

Ext.util.CSS.swapStyleSheet (v4.0, v6.7) function can be used to switch between the different themes, this forums post shows an example.

Also I implemented this at first in my app a while back, but I ultimately found that forcing a browser refresh was necessary instead of dynamically swapping the CSS as there would still be some weird sizing/positioning issues. This was mainly when switching between the accessibility theme.