Task templates are defined on a workflow basis in System settings > Workflow > Schemas. After you have selected a schema to the left, you can find the settings for the task templates by clicking Edit in the task templates category.
Adding a task template
A new task template can be created by clicking (+) in the bottom left corner.
After you have created a template, you can rename it to whatever you like and select what task types should be created when applying the template to an object.
Click Apply when you are satisfied.
Editing or removing a task template
An existing template can be edited by selecting it in the list to the left, modifying it as you like, and clicking Apply to save.
An existing template can be removed by clicking (-) in the bottom left corner.