You can download the current version of QuickTime from:
http://www.filehippo.com/download_quicktime_player/
After it's downloaded and saved, double-click it to start the install process.
It'll overwrite and replace the old version. There's no need to uninstall it first.
--------------------------------------------------------------
Just for your information, don't select "run" when you're downloading files. Select "save" and allow it to download and be saved in your computer. After you've installed the file, you can either delete it or save it for future install.
Creating a folder right on your desktop is the best place to save downloaded files.
--------------------------------------------------------------