Firstly you need to make sure that data is identical on both nodes currently. If data is not identical you should take backup of current master and restore on current slave. Once this is done, you should run the following command on current slave -
mysql> show master status\G;
note down the file name and log position
Then run the following command on current master node -
CHANGE MASTER TO MASTER_HOST='IP of current slave',MASTER_USER='usrname for replication', MASTER_PASSWORD='password for replication user', MASTER_LOG_FILE='file name you noted in above step', MASTER_LOG_POS= Log position you noted in above step;
Now run following command on current master (slave after running above command)
mysql> start slave;
You can check the status of slave with command below -
mysql> show slave status\G;
Now point your application to new master.