How to check the number of updates in the Sales and Trends Module of iTunes Connect
Click Filters, click Transaction Type from the drop down, and click "Updates".
Update 07/06/15: It's still pretty similar: Click Add Filters->Transaction Type, then click Updates.
Update Feb 2020: The filter doesn't offer the "Transaction type" option right off the bat. First click on "Units" on the left panel. Then you will have "Transaction type" as part of the filter.