Using chemical strippers to remove concrete sealer is one removal method, the other is to mechanically remove the sealer by grinding, sand blasting, or sanding it off.
While both these methods work, mechanically removing the sealer will profile, scratch and/or damage the surface of the concrete usually resulting in having to apply a concrete overlay if you want a finished concrete surface.
If you have decorative colored concrete, broom finished concrete or stamped concrete, using a chemical sealer stripper in most cases is probably the better choice.
I'll be honest, chemically stripping sealer, paint, or coatings from concrete is a difficult task. There's nothing really fun about it, it can be messy, smelly, and take hours to complete. But sometimes it is the best way to prepare the concrete for re-sealing or restore the surface to its original condition to repair it or apply some other type of coating.
Chemical removers and strippers come in three categories: bio-chemical, caustic, and solvent-based. You can purchase all three from a Lowe's, Home Depot, Sherwin-Williams or your local hardware store.
Just be aware that all three contain harsh chemicals, otherwise they wouldn't work very well. You need to read and follow the safety information on the label, even the "green" environmentally safe strippers contain chemicals that can make you sick. So be careful and dispose of all waste material in accordance with state and local guidelines.
All these strippers have one thing in common, they need time to work and you have to keep them wet to stay active. Once they dry out they stop working.
Depending on the sealer type and thickness, multiple applications will probably be needed to remove all the sealer. This will take time, maybe hours, so plan accordingly.
Most strippers are in gel form, this helps them hold to the surface better and not dry out too fast, keeping them active longer.
The environmentally safe strippers usually take longer to work, but are safer to use. Protect and cover anything you don't want to strip or kill (plants & grass) and always read and follow the manufactures specifications for best results.
I've tried a lot of different sealer and paint strippers over the years and I've found one that works best for me. Lightning Strip from RadonSeal penetrates and removes sealers and paint from concrete better than any I have tried.
It soaks through the sealer or paint and bubbles it off the concrete. Then you scrape it or vacuum it off. For thicker coatings you may need to do more than one application, but this stuff is great!
Here's a breakdown of the different types of chemical strippers and how they work. This will you help choose the right stripper for your project.
Here's some related information about concrete sealers:
CONCRETE SEALER AND CONDENSATION PROBLEMS
CONCRETE SURFACE TEMPERATURE CAN CAUSE SEALER PROBLEMS
WHAT CAUSES SEALER BLISTERS AND BUBBLES?