This is a very common question on the forum. My suggestion for large areas is to get paint stripper, the citrus based kind, spread it on the floor and give it an hour. Then take a wide blade scraper and scrape it up into plastic bags and dispose. Wipe the residue off with paint thinner or laquer thinner. If the Citrus doesn't seem strong enough, then go to methyl chlorate.
There are also cleaners available for old glue, but it takes a lot and is very smelly. Use lots of ventilation.

We had the same situation and spend hours of labor using a tool from Home Depot but in the end wondered why we did not leave the entire thing down under the pad--would have been just more insulation--unless it smells bad- ours was just incredibly ugly and was thin

Thanks for answering my question. I will try the citrus based stripper. Today I soaked the 6x6 foot area where we had removed the carpet with hot soapy water and I managed to scrape up most of the glue, but it was a lot of hard work. We still have a lot of carpet to remove...but it will be so much better when we are done.

We are going to paint the concrete and add area rugs until we can afford laminate flooring. Thanks again !!! :)

Please post back and let us know how it went. That way we all know if our advice works, or not! Thanks....