Help with permalinks

Using the old classified theme for 4 or 5 years, my site has many listings indexed on the search engines and i can’t afford to lose them. an example of a listing is https://www.mustangtraderonline.com/2012-boss-302-laguna-seca-for-sale with the domain name followed by the listings title.

with the new responsive classified theme, i can’t figure out how to get rid of the /listing/ in front of the listing title. the new URL would look like this – https://www.mustangtraderonline.com/listing/2012-boss-302-laguna-seca-for-sale. This would cripple my site. I see where i can change the word ‘listing’ to something else but when i try to change it to spaces, it reverts back to ‘listing’.. do i have to change coding somewhere?

Thanks.