Evolving heroes to 7 stars

My heroes has 6 stars, says that it has reached max evo why? When can i evolve them again?

To evolve your heroes to seven stars, you need to do an upgrade (research) with the help of legendary runes, like you with ancient runes to improve milestone rewards and energy output.

Click on the hero in the home screen to do the upgrade

I dont get it?where do i make research?

Sorry for using confusing terms.

In your Home tab → goto player (the hero standing in bottom left) → goto powerups ->see the section “advanced powerups”. Put legendary runes in there to level it up. After it completes new powerups will be visible and after some time, you will be able to get the hero level capacity powerup.

Refer the screenshot below