Whatever you do stay away from hot solvents like lacquer thinners, mineral turps. acetone or hardware stores paint strippers concoctions - they may shift the paint but will also dissolve the plastic underneath.
If it's an acrylic paint you could try soaking the model in 99% rubbing (isopropyl) alcohol - this shifts many acrylics quite efficiently.
If you have an enamel paint job to remove then a strong caustic soda solution will usually work very well. Make sure the solution has cooled down unless you want a banana shaped model - mixing NaOH in water releases a lot of heat. It may also cause some glued joints to come undone so sieve the waste carefully if you have a lot of small parts to save
If none of these work you may have to try one of rhe commercial plastic friendly strippers such as Easy Lift Off, and if that doesn't work consider investing in a home media blasting set up - used sensibly with a blasting medium like baking soda or walnut shells this sort of set up will move most paint and leave the detail behind.