You can use netsh commands to change DNS settings on most of the modern Windows OS'es. The commands below changes the DNS servers of "Wireless Connection" adapter to Google's DNS's.
netsh interface ipv4 set dnsservers "Wireless Connection" static 8.8.4.4
netsh interface ipv4 add dnsservers "Wireless Connection" 8.8.8.8
The problem is that you need admistrator privileges in order to execute these commands. It doesn't matter for Windows 7 even if you are a local admin, you need to get escalated privileges.
One solution is to save the above commands in a batch file, say "dns-google.cmd" and run it with right clicking and selecting "Run as administrator".
Another solution is to use elevation power toy. You can download it here. After extracting the archive to a location, say C:\Tools\Elevation, create another batch file with contents similar to this:
C:\Tools\Elevation\elevate.cmd dns-google.bat
It will ask for administrator right if you don't run it with right clicking.
BTW, the command below will change the connection to use DHCP issued DNS servers:
netsh interface ipv4 set dnsservers "Wireless Connection" dhcp
