This can be a very tedious task and a lot of people avoid doing it because if not done properly it can ruin the finish of the model. However, avoiding this step if the paint has been applied thickly can cause the model itself to lose vital details, such as the eyes and not just muscle tone! There are many ways to strip and I am by no means an expert (I HATE stripping but I think I have finally found a method that works now) but I use this paint stripper that I believe I bought in UK's Homebase store last year or so.
I use a toothbrush and apply it to the model, leave it for a couple of minutes or so and then I start scrubbing! It can be quite therapeutic if a horse you have has paint it really needs to get off!
However, I must advise, I wouldn't leave it on for more than 30 minutes or so. I had a mini resin kept in a sandwich bag with this stuff for a couple of hours and the stripper got into the plastic of the model, and I could physically scrape away the resin with my fingernail! it was scary... I left the model to 'dry' but it was never the same again. So don't do that! Live off experience. At least I know now!
This model I am in the middle of stripping at the moment, it is a Peter Stone ISH and is a commission piece. Please excuse his head not being present! The primer on this model has actually been applied very thickly and I am having difficulty with getting it off, I just need some more elbow grease! :-)
I used to hate stripping horses, I could never do it... When I first got into the hobby, I heard rumours about nail varnish working a treat for stripping horses, and yes I used it. But I would not recommend it at all! The acetone eats away plastic in a much more aggressive manner, and all the details can disappear and be less visible than with the paint on in the first place!
Other hobbyists I know also use oven cleaners to get rid of the paints on their models. I personally have never used this method and so can't comment, but I have heard it works a treat and maybe if I know of a tutorial or images somewhere that someone has done online, I could seek permission to share it on here with everyone.
I hope this Tip Tuesday was useful, I certainly remember when I first joined the hobby that stripping was a very daunting process. I have come all this way in the hobby through self teaching, trial, error and constructive criticism from other helpful people. I hope that what I have learnt and what I put into these posts is useful for everyone!