Note: We've just updated the name of "Match Type" - it's now called "URL Scope".
See here for a full overview of exactly what our URL Scope (aka "match type") options mean.
How to configure URL Scope to change rankings match type
From within a campaign, click "Settings" on the bottom of your left side menu.
You should now be on the Campaign Details page, if not, click Campaign Details from the settings page menu.
The match type can be configured by changing the "URL Scope" setting. When you're done, click "Save" before leaving the screen. You may need to scroll down to find the save button, in the bottom left.