In order to change the adjective into the superlative form in Spanish, it is necessary to add syllables and modify the ending of the adjective, but you need to pay attention to the subject to respect the gender.
The adjective is BELLA so you have BELLISIMO and BELLISSIMA.
For example: El cuadro es bellisimo ( cuadro and bellesimo male gender)
La historia es bellisima (historia and bellisima female gender)
You might have number changes as well when using the plural. BELLISIMOS/ BELLISIMAS.
