Drop table columns that are constrained

You have to remove the constraint and then to drop the column.
To know which is the constraint you can generate the create script of the tabler using SQL Server Management studio, and then drop the costraint (again you ca do it from SQL Server Management studio, navigating the tree view under the table -> constraint)

I dont really understand why you are trying to delete this column. In case, some foreign key constraint is defined on this column then u need to find the columns which is related to this columns , if you need to delete those columns also, drop them all first , then drop the constraint and that particular column

Actually, problem is that when I do replication, database is automatically added one column (rowguid) on every table with a lot of constraints.Now I want to drop this column in order to export file.