To change your PDF viewer follow the steps below:
1) Right click on a PDF File and select "Properties"
2) Click Change
3) On the Menu select your preferred PDF viewer/editor, select it and click OK
4) This will bring you back to the properties window, you should see that "Opens with" has updated to the program you selected
5) Click on OK to close the properties window.
If you need any assistance with this please contact the Support Desk by calling 0117 933573 or emailing firstname.lastname@example.org