i have been trying to change the presentation for figures separating the cents with commas and every three figures with commas as well. Not working, can you advise?

I appreciate you trying to change the presentation for your figures, Fernando.

It's possible that these changes weren't applied correctly. Make sure to click the Save button before selecting Done.

I've added a screenshot for your visual reference: 

On the other hand, I recommend clearing the cache and cookies because it will remove accumulated data that also blocks web pages from performing. Ensure no other users are making simultaneous changes to avoid conflicts from the updates made. To update number formatting, click on the Gear icon, select Account and Settings, go to the Advanced tab, choose the desired Currency format from the dropdown, then click Save and Done.

Another important point is that, you can also consider turning on multicurrency if you're dealing with customers worldwide in QuickBooks Online (QBO). 

We're always here to help if you need further assistance to any of your QuickBooks concern.