To find a string in a certain field and replace it with another string:
update [table_name] set [field_name] = replace([field_name],'[string_to_find]','[string_to_replace]');
Attention in classroom
To find a string in a certain field and replace it with another string:
update [table_name] set [field_name] = replace([field_name],'[string_to_find]','[string_to_replace]');