Step 1 : 
http://www.google.com

Step 2:Now enter this dork (this is Dork for find DNN Valn sites)

        or
   inurl:/Fck/fcklinkgallery.aspx

this is a dork to find the Portal Vulnerable sites, use it wisely.

Step 3: 
it will show you many sites, Copy any one of site.

Step 4: 
For example take this site.
Example:


http://www.itservicespro.net
Step 5: Now Paste after the site url
  this

so Site is this : 
http://itservicespro.net/Providers/HtmlEditorProviders/Fck/fcklinkgallery.aspx

so it will look like this (screenshot below)
Note:  if it will show you like this (see screenshot below) its mean site could not hack find another site
 

Now Click on File ( A File On Your Site )

Step 8:Now replace the URL in the address bar with a Simple Script

Step 9:You will Find the Upload Option

Step 10:
Select Root

Step 11:
Upload your shell ASp Download it here
After upload 
go for your shell  www.yoursite.com/portals/0/yourshellname.asp;.jpg
EXample : http://www.itservicespro.net/portals/0/umer.asp;.jpg
so you upload shell and shell is front of you look like this (screenshot below)
Click on <Dir>...  again and again till you will see admin
 so when it will show you this page admin area page click on UPLOAD FILE TO C:\WEBSITES\WWW.ITSERVICESPRO.NET\WEBSITE\
and upload your deface index page so
this is your result www.site.com/urpagename.html
for example see this http://www.itservicespro.net/umer.html 
If  you want to deface main page then click on Admin dir and search for index htm or html and click on Edit and copy your deface page code and replace there...:)