Provided that the uninstaller is well-behaved, then uninstalling the program will revert the associations to their previous values.
If you want to keep the program, but still want to revert the associations, you can do it manually for each file type:
Right click on a file, choose "open with"
Choose the program that you wish to open it with and check the "always use this program box"
In future, when installing new software, read each screen carefully before clicking the "next" button. Almost all programs will ask your permission before changing any associations.