Please do this using the network cable that came with the cd or any other network cable you got to set the router.
By default you can access the router setting using your web browser. But I think d-link has the setup cd where you can set the wireless setting at the same time too.
Anyway just go to your browser and key in http://192.168.1.1
which is the default gateway, if you can't access then the person who set your router has change it. Click here to to find out your gateway
Your be prompted a log on popup as you enter then address and by default it should be (Username: admin / Password: admin). You should be able to see a few tabs on top and on your first is the setup tab. At the same tab choose "Wireless Settings" which would be somewhere on the left side penal on the setup page.
Click the "Wireless Settings" and you get a page with 2 button, choose Wireless Basics and in there you can change the SSID. Once you changed don't forget to click "Apply" button somewhere at the bottom of this page.
You should be able to see the new wireless SSID on your laptop now or desktop.
Can see the manual here online: D-Link Manual for DSL-2640B