First you must upload these 3 images to your hosting image service.Replace "URL of your own image" with your real Urls.

1.Log in to your dashboard--> layout- -> Edit HTML

2.Click on "Expand Widget Templates"

3.Now follow these steps to replace codes :-

(A)Scroll down to where you see this:-

<data:newerPageTitle/>

Replace above line with

<img src='URL of your own image'/>

(B)Scroll down to where you see this:-

<data:olderPageTitle/>

Replace above line with

<img src='URL of your own image'/>

(C)Scroll down to where you see this:-

<data:homeMsg/>

Replace above line with

<img src='URL of your own image'/>

4.Click on "Save Templates" and Refresh your site.