The way that Moodle 2.4 handles uploaded files has changed: files can now be easily embedded into a Moodle page for viewing. When uploading new files you can select how the link will behave, however some of you may wish to change the behaviour of an existing file.
In the example below I change a .pdf file from being displayed embedded in the page to opening in a new window.
Locate your resource on the course page and click the cog icon to edit ("update") the resource:
On the menu that follows you will see the resource name and a white box for a description- if this is empty you must enter something here- in Moodle 2.4 this is a required field as the resources will appear as a list for the course (if the name is self-explanatory I have just copy and pasted it here again on occasion).
Below the file selection area is the Options block, here you need to change the drop-down menu to your preference- in this example Open.
Click 'Save and return to course' and check that clicking the link does what you expected.