Good options for removing wax from a car include detailing clay, solvents, pre-wax spray cleaners or non-abrasive polishes. Detailing clay and non-abrasive polishes deep clean a car's paint in addition to removing old wax. Spray cleaners are easy to use, but don't remove deep contaminants.
Prior to wax removal, thoroughly wash the vehicle. Rasky's Auto Detailing in Minneapolis, Minnesota recommends using CG Citrus Wash N Clear, which, depending on mixing ratio, may also remove old wax. Use cleansing products specifically designed for cars if possible.
Regardless of wax removal option, always work on one small area at a time. When using detailing clay, spray the area with clay lubricant spray. Either apply soft clay to the prepared area or rub a moist clay bar over the wet area. After removing the clay, wipe the area with a microfiber cloth, using the lubricant spray to remove any remaining clay. Repeat until the surface feels smooth.
Pre-wax cleaners such as P21S Paintwork cleanser or Pinnacle Paintwork cleansing lotion add depth and gloss in addition to removing wax. If using solvents, remove them as quickly as possible to avoid damaging the paint. Regardless of the wax removal method, only use microfiber cloths for removal. Cotton is likely to scratch the finish.