Transform 12,50 in 12.50

[magicool]

Hi,
In a workbook some of the numbers I have to use are in format: 12,50. How can I modify the formula so it transforms it to 12.50 (so that excel knows this is a number)? I am getting the values with:

=VLOOKUP(F1,Sheet1!$A:$B,2,0)

and all the values are with "," instead of "."
Please check the example attached.
Thank You!