Can you open the photo in anything? what happens if you double-click it? If it shows on your screen, search the menus for something that will either resize (say by 50%), or perhaps let you save as or export as .jpg, and then you may be able to specify a file size (smaller than whatever it is now.)
If that doesn't help, and if you don't have a video editing program, you can probably do it in MS Word. Open a new Word document, and import the photo. I don't know the specific menu/command under Windows, but look under Import, or maybe Open, or perhaps Format / graphic. Then find the photo and click Open or Import.
Once you have the photo on the screen, if you click or double-click it, you should be able to resize it by putting your mouse on the lower right corner and then moving diagonally up to the left. On a Mac you can hold the shift key in while resizing, so the proportions will stay the same - I don't know about doing that in Windows.
You may also find something under the menus, perhaps under format/picture or format/graphic that just lets you specify the amount of reduction - e.g. 50%.
Then see if you can export or save as... a .jpg file.