How do i increase the total MyISAM indexes?
Your key_buffer_size is way too big.

Since your MyISAM indexes is that small, set it to 128K.

You need to open my.cnf and add this under the [mysqld] group header

[mysqld]
key_buffer_size = 128K;


You don't need to restart mysql. Just run this

SET GLOBAL key_buffer_size = 1024 * 128;


Give it a Try !!!

Based on the mysqltuner output, you can drop the innodb_buffer_pool_size to 3G.

For more clarification on sizing MyISAM and InnoDB caches, see my old post What are the main differences between InnoDB and MyISAM? on how to compute the ideal sizes for both MyISAM and InnoDB.