Fatal error encountered on my main WordPress admin login

1. If you have access to your PHP.ini file, change the line in PHP.ini
If your line shows 64M try 128M:
memory_limit = 128M ; Maximum amount of memory a script may consume (128MB)

2. If you don’t have access to PHP.ini try adding this to an .htaccess file:
php_value memory_limit 128M

3. Try adding this line to your wp-config.php file:
Increasing memory allocated to PHP
define('WP_MEMORY_LIMIT', '128M');

4. Talk to your host.

5. Deactivate/remove some plugins if you still have problems (rename the plugins folder via FTP if you can’t access the dashboard).

Tried to do as you said but this time got the following new fatal error instead :

Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 19456 bytes) in /home/yeng29/public_html/zendevi.com/wp-content/themes/enlight/functions.php on line 1056

Already sent a support ticket to my host about it, but could you tell me exacly where to insert the 2 lines of code you mentioned above in (2) & (3) ? i.e. which parts of the .htaccess file & wp-config.php file must i insert those lines of code ?

Thanks alot.