If you look for brakes in the Panda section using the search option on one of the top menu bars, you will find threads like these:
https://www.fiatforum.com/forum/topic.asp?TOPIC_ID=1798
https://www.fiatforum.com/forum/topic.asp?TOPIC_ID=901
and another one like this:
https://www.fiatforum.com/forum/topic.asp?TOPIC_ID=10102
when I changed my mind a bit about things...
General view from me is that if everything is absolutely spot, on the brakes are quite adaquate for the stadard Panda (but can need a substantial push in an emergency situation).
Usually, when someone says their Panda brakes are no good they are running with less than 50% of the intended stopping power.
If you can lock both front wheel on a dry tarmac road at 30 mph there isn't much wrong with them
If that isn't enough, you could fit a servo - which some variants and later models had as standard.
If you get fade from very high speeds you might need drilled disks, and/or fancy pads.