If you want to disable the mobile version of the site (this will disable mobile version of the site for all devices), search for this line in the web.config:

and change to this:

We need to check how we can disable mobile site just for some devices.

thanx but like I mentioned in my question, I don't to disable the mobile site completely.. I want to disable it only for tablet like android, window And ipad....so please help...

There are two settings that can go in web.config that can be used to achieve this. You can insert them and adjust their values to fir your needs.
MobileBrowsersPattern has the following default value

MobileAppsPattern has the following default value
As you can see, both are regular expressions that match the browser or device name received from the client.  

thanks for sharing denis, but this information is little overwhelming ...I don't see any values that are specifically for tablets (android, windows and ipad)- I would deeply appreciate if you could guide me with this and point me where exactly to put this information in what manner ?

By default, iPad users are not redirected to the mobile site. You can't just remove "android" alltogether, as some android users are coming from the phones, and others are using tablets. The same holds for windows. You will need to go through a list of the devices that need to access that version and remove them from the regular expression, or alternatively remove "windows" and "android" from the expression and insert the names of the devices that need to use the mobile version.
Is can be a painstaking task, but that's just a way it is. You can alternatively use WURFL or a similar database to redirect the requests on your own.

Could you please show me how these 2 settings will go in web.config file and where ? Can you please show me an example ?

Just place the following in the appSettings section of the web.config