Solved Button

How do i put the Solved Button over the topic icon?

Admin Panel => Display => Pictures and Colors => Pics management => Advanced mode => Click on "topic Icons" => Now click on the "create" button and add them there.

i did this but my icons appear next to the topic icon look at This

Thats because you are using phpBB2 and only in phpBB3 you can have the solved icon over the buttons.

Edit:
just like here on the support forum.

if i change to phhpbb3 do i lose things like CSS ?

you can save your css code before your are doing that and you can switch to phpBB3

does it have more advantages then phpbb2 or is it just almost the same?

This may help you => https://help.forumotion.com/manage-the-appearance-of-your-forum-f45/what-is-the-diffrence-between-phpbb2-phpbb3-punbbinvision-t67343.htm?highlight=what+is+different+from+phpbb2+to+phpbb3