I want to change the custom back button in sherlock action bar and remove app icon

I want to change the custom back button in sherlock action bar and remove
app icon

I dont like the default back button that comes with action bars they look
rather to tiny for my liking. I trying to fix a bigger and more
descriptive button like the one used in the WeChat Mobile App. please any
body with an Idea.
I tried this below but did not work
<item name="android:homeAsUpIndicator">@drawable/back</item> //Put in my
style
The the one below in my code
ActionBar actionBar = getSupportActionBar();
actionBar.setHomeButtonEnabled(true);
actionBar.setDisplayHomeAsUpEnabled(true);
// actionBar.setDisplayUseLogoEnabled(false);
actionBar.setDisplayUseLogoEnabled(true);
But did not work. the image that I kept in my drawable is not show. My app
icon keeps show on the action bar which I dont want. and the back button
is not working. Please any idea.