Change the following entries in your web.config file located in C:\Program Files\MindTouch\MindTouch Deki\web\web.config:
post_max_size = 256M upload_max_filesize = 256M
Go into Deki Wiki control panel -> Configuration and set
files/max-file-size
to "268435456" (for 256MB)
Note: The configuration screen is introduced in Hayes+ 1.8.2. For previous versions, you'll need to make a direct database update into the Config table and restart dekihost.