Help my friend get a tattoo

Hello!

My friend wants to get a Japanese tattoo saying something like "self improvement" so of course he found 改善.

I told him it was not the right word to use. It sounds like he's getting a tattoo saying the Toyota method" or something like that.

Am I right?

And if someone knows, is there a word he could use that would make more sense?

I'm not very good in Japanese yet, but I don't want him to get a dumb tattoo and look like a dumb 外人 lol.