If your DBMS does NOT have a “replace” function, you will have to use character substitution using several string functions.
Here is an example in Sybase and SQL Server.
SET YourColumn = stuff(YourColumn, patindex(YourColumn, ‘%’), 1, NULL)
This says find the pattern of ‘%’ in YourColumn. Now use that position number and replace aka stuff the character with NULL instead.
Good SQL, good night.