Removing floor adhesive from concrete can be a very difficult task. Besides your tools, you will need a lot of elbow grease. Remember, the flooring was meant to be there permanently, so the adhesive won't give up easily. Patience and perseverance is the name of the game when it comes to this project. If you have those, you will eventually win the war of the stubborn adhesives.
Use a floor scraper and scrape, scrape, scrape. You can rent an electric floor scraper or you can use a manual one. Electric floor scrapers are a little hard to control. You may want to ask to try one before you pay to rent it to see if it is a tool you can use. Get as much off as you can. It will be a lot of work and make your muscles hurt, but keep scraping until you've gone over the whole floor.
Take a 4-inch razor scraper and go back over the floor, trying to get right down to the concrete. You may have to go over it a couple of times. Keep the blade sharp by changing it every once in a while. You'll be able to feel when it starts to get dull.
Try Krud Kutter or acetone. You can buy both of these in your local hardware or home improvement stores. They are solvents and should be used with care. Use gloves, protective clothing and make sure you wear eye protection. It can easily splash and get into your eyes. Read the manufacturer's directions on how long to let it sit on the adhesive. Pour it on, let it sit and scrape it off with the razor scraper. You can use a wire brush attachment for your drill if it's really stubborn. If you need more leverage, use a 5-inch putty knife and get down on the floor and scrape with it. Make sure you rinse the floor well and get all of the chemicals off of the concrete when you are done.
Use some boiling water. Sometimes the glue will soften when boiling water is placed on it, and it will be easier to remove. If you have already tried the chemical solvents and there is still some adhesive left, try boiling water. Make sure to put a towel around the area to keep the water from going everywhere and do small sections at a time. The chemicals may have loosened it some and the boiling water may finish the job. Most of all, just keep at it. It will eventually come up.