Hi Uwe, 

Thanks for your query. Minitab uses the Regional Setting  Windows
Control panel to specify the decimal separator to be used in the
worksheet and the corresponding output. Therefore the only way to adjust
this is to change the settings in the control panel. 

Go in to the Control panel and select 'Regional and Language Options'
select the Customize button in the Regional options. You must exit
Minitab and re-launch for these settings to take effect.

Hope this helps. 

Kind regards,
Eugenie Chung 
Technical Support Specialist

Minitab Ltd.
Unit E1-E2 Brandon Court
Progress Way
Coventry
CV3 2TE
United Kingdom