For ImageJ Go to https://imagej.nih.gov/ij/ and note, you can now run the Online version at https://ij.imjoy.io/ it will run independent of your computer, this is the preferred method.

If your computer has java installed download the platform independent version, unzip the folder and launch ImageJ from within the folder. If your computer does not have Java installed, download the ImageJ bundled with Java, unzip the folder and run ImageJ from within the folder. Note, make a short cut of ImageJ from the folder onto your desktop.

For Fiji Go to https://imagej.net/software/fiji/

To use the following you must have Java preinstalled onto your computer. Download ONLY the version without Java, "Platform Independent" for ImageJ or "No JRE"  for Fiji and save to your download folder. Extract the .zip files to your My Documents, Documents or Desktop folder. Locate the folder, open the folder and find "ImageJ.exe" for ImageJ or "ImageJ-win64.exe" program for Fiji, make a shortcut of the program on your desktop. Open ImageJ or Fiji from the desktop shortcut.

Tech notes. In a managed computer environment users are restricted, they cannot install programs. Java is a well established program used in a multitude of applications, it is also a widely exploited program and therefore used to compromise computer security. Allowing IT security to manage Java on your computer and running the platform independent or no JRE version is the best compromise between meeting computer security needs and delivering a users ability to use ImagJ and Fiji tools.