If you are running a version of windows prior to 7 which in itself is outdated... you can make this work under Vista SP2 by downloading an older build of imagemagick portable from http://martinleese.epizy.com/MyTemporaryDownloads/?i=1 down in the section to keep XP going it's a multipart 7zip archive of a ZIP archive so will require double extraction or after downloading all the parts open the first part in 7zip and extract the convert.exe and replace the windows 7 and above build in the data sub folder of the installation directory and your ready to go it should even work in XP though only tested in Vista SP2+ this is the first HEIC converter I have installed purely because it's not an expiring trial license. I don't have any Apple devices but one day I might need to convert an HEIC/HEIF file sent to me or sent to a relative that they don't know how to handle.
I do note there is a samples subfolder in the installation but for some obscure reason the developer has chosen to leave the folder empty rather than include a couple of sample images to try it out.
It not only supports JPG and PNG it also supports TIF, BMP and GIF too so is more than just HEIC To JPG It is just a GUI on top of the imagemagick convert.exe program but it appears to work ok with samples downloaded from the internet producing mostly compatible output. There is a so called portable edition but it gets it's license status from the registry of the host computer and does not store and re-use the activation data within the portable folder so it is not fully portable but does recognise and re-use the registry giveaway license key.

Thanks for the Lifetime License! There have been a few HEIC Converters offered on this site recently but they all had very short License Terms, so this is very much appreciated.

For anyone wondering where to enter the License Key provided in the ReadMe file (the best, and easiest on the receiver, way to offer a giveaway!) (Thanks for that as well) just click on the "Upgrade to Pro" link in the lower right. It will open your browser, but just close it and the program has the Registration window waiting for you.

I only need to convert HEIC once in a great while because I maintain a bible study website for an old friend who keeps sending me HEIC pix to upload, but I don't own a smart phone and they are so computer illiterate they don't understand why I can't use them!

Now I'll never have to demand they learn the basics of file formats, and which can be used on the web, ever again.