To change the category of a group of transactions, head to Transactions and select the magnifying glass icon where in the next screen you can select the category group you wish to change from the category dropdown menu.
Perform action will appear once this has been selected, select this and then select Re-categorise.
The Perform action option will only appear if there are less than 100 transactions. If there are more than 100, please use the dropdown menus to lower this number.