Application Express :: ORA-01439 / Column To Be Modified Must Be Empty To Change Datatype

I need to modify the column type that already has data in it, i need it change varchar to number then The datas entered have $ and , (e.g $3,200). I need the $ and , removed with column type set to numbers.

When i currently do this i get the following error:

The TABLE operation was not successful for the following reason:

ORA-01439: column to be modified must be empty to change datatype

I've tried unloading the data and loading the data using the spreadsheet, cut and past and csv file but both give me more errors, so i just want that one column modified.