装饰 as a verb means 'to decorate,' as a noun means 'decoration.' 装修 (zhuāngxiū) is more specifically 'to renovate/remodel' (a home), while 装饰 focuses on the aesthetic touches.
usage
Common compounds: 装饰品 (zhuāngshìpǐn, ornament/accessory), 室内装饰 (shìnèi zhuāngshì, interior decoration).