I took a look at the site and the only place I noticed it opening a link in a new window was on the Links page. That is the one place where I and many others prefer to open a new window. Since you are going offsite with those links, it is frequently preferred to open a new window.
A. It tends to let people know they are going offsite.
B. It makes it easier to get back to your site by just closing the window rather than hitting Back button 10 times.
But if you want to open these in the same window rather than a new window...here is a copy of your current html for "Jotika Models" from your links page:
<a href="http://www.jotika-ltd.com/Pages/1024768/index.htm" target="
_blank">Jotika
Models</a>
As I mentioned before, you need to change the target="_self" to target="_self" as in the example below:
<a href="http://www.jotika-ltd.com/Pages/1024768/index.htm" target="
_self">Jotika
Models</a>
Hope this helps.