This depends on your version of IIS
You may view Chris Hammonds video here,
http://www.dotnetnuke.com...in-DotNetNuke-6.aspx which shows you how to do this. This post will just give you the quick basics.
http://bit.ly/dnnlarge For IIS 5, or 6
Edit the web.config file for your application.
Change maxRequestLength="8192" to maxRequestLength="81920" (for 80MB)
Change requestLengthDiskThreshhold="8192" to requestLengthDiskThreshhold="81920" (for 80MB)
Save the web.config. You are finished here
For IIS 7
Change maxRequestLength="8192" to maxRequestLength="81920" (for 80MB)
Change requestLengthDiskThreshhold="8192" to requestLengthDiskThreshhold="81920" (for 80MB)
AND you need to add some new code in the web.config file
Search for the system.webServer section
Paste this code before the closeing </system.web> tag
<security>
<requestFiltering>
<requestLimits maxAllowedContentLength="83886080" />
</requestFiltering>
</security>
which is measured in bytes
Save the web.config. You are finished.