change varchar datatype of the 400 datefield to date

I have a table with over 2000 column, about 400 columns of the the 2000 are datefields in varchar datatype. Now I have a task to change varchar datatype of the 400 datefield to date, bearing in mind that some out of the 400 datefields are in datetime. I want the date to be set to DMY with 24 hours time. can someone help please?