C# - Change Image On Postback?

So, here's the scenario: I have a page in my asp.net c# based website, which displays data dynamically after taking the request from query strings.For example:

Brand=HTC&model=Wildfire

Now, in this page I want to display all the deals available in each network separately.So, on the first pageload, I retrieve the data from the tables of each network that has the requested handset in a deal, store it as a datatable in the cache.I have a datalist for displaying the imagebuttons of the networks that have the deals of that handset. The user will click on the imagebutton of a network to view the deals of that network.

To display the deals, I am using a gridview which retrieves its datasource from the cache. Also, I have provided filtering of the rows through dropdowns in each columns' header of the gridview.All this is inside an updatepanel.
Everything's working fine.

The Problem: I want that whenever the user clicks a network's image button, an image should appear above the gridview, containing the logo of that network.

Things that I have tried: I am storing the networkname in the cache(which also required for filtering the gridview), whenever an imagebutton is clicked. Then, on pageload, I'm doing this:

if(ScriptManager1.IsInAsyncPostBack)
{
Image img = new Image();[code]...

where, nw_image is a tablecell which i'm using to display the selected network logo.and also I've saved the network logos in the images folder as: 'network'_logo.jpg eg: 3_logo.jpg, orange_logo.jpg

The result of this is that when I click a new image button, the image that is displayed is that of the previous network, i.e. the cache is always one postback late.