possible to have custom banner installed on iNove theme?

hi, i have a wp 2.71 blog running the iNove theme, the blog can be found at http://happy-paws-grooming.com , i want to get rid of the text that is where the banner normally is and have a custom banner created. firstly can someone tell me what size banner i would need and in what format? And is this an easy job to do or are technical skills required? really love this theme but just want a custom banner to make it look nicer.

hope someone can help

thanks guys

alan