its a basic SQL command but require help ?

I have a small sqlplus problem. i have created a table with date field along with other varchar2,number etc. But unfortunately i made a mistake in entering the date. for some date records i made an error in month... say for 20 record.Now i need to correct the month.HOW????

i have tried with 'update' statement using like,=,... etc.All resulted in failure.i thought of converting date datatype to character and then use the 'update'.But its not working.What shall i do now ? should i correct each and every record . Is this a drawback of Oracle????