Left-click on the "Edit page" tab of the page you want to change.
Put the cursor in an appropriate line.
Left-click on "Attach file" on the top right menu bar
You can browse your hard drive and Upload your file onto the wiki.
When it is finished uploading click on "OK"
You can change the wording of the link while in Edit mode if you want.
Click on "Save" to exit the Edit mode.