How to change Text to Number in Excel 2013

Hi,

I imported and parsed a large CSV file (75000 rows) with 4 columns as numbers. They arrive in Excel as text with a "." as decimal separator. In Excel options, I set the decimal separator to "." but data remains as text. I could edit and enter each cell to convert it as number but I have 4 x 75000 cells...

Any idea ?

Thanks for your help