Mysql how to change a constraint from on update restrict on delete restrict to cascade

Question

I have a table and I added a foreign key constraint to it by this statement

ALTER TABLE `t_Accounts` ADD CONSTRAINT `Relationship51` FOREIGN KEY (`Account_Group_Id`) REFERENCES `t_Accounts_Groups` (`Account_Group_Id`) ON DELETE RESTRICT ON UPDATE RESTRICT;
 

Now I want to change it from just ON DELETE RESTRICT ON UPDATE RESTRICT to ON DELETE CASCADE ON UPDATE CASCADE. How I can do that.