Best method to remove old paint

What is a best method to remove the old paint without scoring or ruining the actual plastic?

The best way to do this is by using a paint thinner(not paint stripper). The best thing to do is to purchase the paint thinner at a hobby shop because then at least you'll be certain the paint thinner is designed for plastic model kits. Using this will in no way score or ruin the plastic, at least I've never known it to. Depending on how many layers of paint there is, you may need more than one application. Also, if the paint is very old and has been applied for quite some time, there may be some staining of the plastic meaning that there might be some discoloration of the plastic even after all the paint has been removed. To apply the paint thinner you can use cotton swabs(preferably), facial tissues or Q-Tips for small or hard to reach places.

And you can find the answers from related articles from another sites:
How to remove paint from plastic models

Thank you and best regards, see you soon.