Dye textiles lighter?

I'm moving into my first apartment soon. It's from the '80s and furnished accordingly. I simply painted a lot of the furniture and gave it a bit of a contemporary makeover to save money.

I'd like to do the same with the curtains on the window. These are dark blue and made of 100% cotton.

My question is whether it is possible to recolor them to a light gray.

I've heard that it's not possible to bleach the curtains first and then re-dye them, as the bleach will damage the fibers, preventing the new color from sticking… Is that true? I've also read that you should treat the fabric with a bleach first. But that only works on fabric that's discolored from washing, right?

I'd like to do it right from the start so I don't end up buying paint, bleach, etc. for nothing.

Thanks in advance for all experiences and tips!