How do I turn off always open files of this type?
For chrome the setting to turn this off is Settings -> Show Advanced Settings -> Downloads -> Press the button to clear automatic processing. It will be different in each browser but basically in settings.
How do I remove the default application of a file type?
Go to Settings.. select Apps and then select Default Apps which is listed on left hand side of the page. Go to the bottom of that page and click on Default Apps by file type.