Multistar does not have a centralized global website. Instead, the updates are hosted on OEM platforms. Here are the for your download.
"Multistar" is a brand name that covers a wide range of DVR boards and standalone units. Using firmware intended for a different model will likely "brick" the device, rendering it unusable. multistar dvr h 264 software upd download
Before downloading any software, you must confirm your exact hardware model to avoid "bricking" the device. Multistar does not have a centralized global website