How can I change number format in my PC (Windows 8)?

I am using Windows 8 and have a number format that uses commas instead of dots for numbers (for instance, in Excel I have to write 3,45 in formulas instead of 3.45 or I get an error).

I remember changing it on Windows 7 via some control panel setting on the bar at the bottom of the screen, that changed also date format, hour format (from 24h to 12h format) and other standards all together, however I cannot find the same option on Windows 8.

How can I do this? I would like, if possible, to change all formats (date, numbers, calendar) to US standard. Changing only one thing (say number format) would be ok, but changing all formats is strongly preferred.