If you select all of the columns you want to change, you can then go to the pull down menu
Cols==>Standardize Attributes
In that dialog, you can change both the Data Type and the Modeling Type. Make sure you change the Data Type first. Character data is always Nominal, so if the columns you are attempting to change the Modeling Type are not Numeric, you will not be able to change them to Continuous. BTW, I assume that is the issue with your latest posting too.
Jim