Workflow Form alerts must be changed through Workflow Form Designer.
Log into Workflow Forms Designer
Select the relevant form and click Edit
On the Approval tab, select the stage you want to make changes to and click Edit
On the Alerts tab, select the relevant alert and click Edit
You can now update the text as needed. Field names which begin "[\\" can be selected from the list on the right and in the actual emails will be replaced with the real life values
Once you have made all of your changes, click Save on all open windows.