Med and Large images not showing - NEW

My zen cart was preloaded as a package am now tring to add new product lines. Zen Cart 1.3.8a, have looked over the past 3 weeks at all forums and tutorials - cannot locate what I need - please help - new at this - know some html. Adding new product images on my computer - all sized, optimized and named per Zen Cart forums loaded small photo 120x120 with product upload button into Main Page option. loaded large photos (height 480px) into large image folder with product code + LRG (ex:1234_LRG.jpg) and same for MED images- through Cpanel. small one shows up fine on product lising page - but the individual product pages and large option are all the small image. Then I tried loading all through the product atributes page (putting LRG into dropdown Large - etc.) strange - but thumbnail ok on listing - on Product page the URL is my website/images/medium/1234.jpg (small showing not image with _MED.jpg ) =- same for LRG - MED folder but small photo. Think cart configured for stuff already on site - what can I do - the preloaded photos are located at the host site - do not conform to the MED and LRG file criteria of Zen cart interface.

make sure medium images are in folder
/images/medium and
large images in
/images/large

wow - thanks for replying - worried with all the image threads this one would be discarded! - attaching jpg snap shot of cpanel folder - photos are in their correct folders (forget that the additional photos are not showing up - worried about the main LRG and MED ones now) - Thanks again for your patience - (did not attach as photo)

Follow faq/tutorial at
https://www.zen-cart.com/tutorials/index.php?article=58

I appreciated the suggestion and to make things simpler - I removed all multiple images - now have: ex: 11-122_catalog.jpg (thumbnail) entered through the product attributes page. have 11-122_catalog_MED.jpg uploaded to MED image file. have 11-122_catalog_LRG.jpg uploaded to LRG image file both through Cpanel. I still only have the small or thumbnail image showing for all image place holders: in the general listing page, the product page and the enlarge photo with pop-up window page. Seems the links are not right - would you please help me trouble shoot this - don't know where to start except "go to" the Cpanel. Thanks - I really appreciate your time!