CE 2.2.5 upgrade fatal error

[WZ_OZES]

Try to upgrade to Magento CE 2.2.5 again today. End up with below error

"mmap() failed: [12] Cannot allocate memory

mmap() failed: [12] Cannot allocate memory

Fatal error: Out of memory (allocated 837816320) (tried to allocate 10485792 bytes) in phar:///usr/local/bin/composer.phar/src/Composer/Util/RemoteFilesystem.php on line 292

"

This happens in the middle of upgrade while "- Updating magento/magento2-base (2.2.4 => 2.2.5): Downloading (50%)"

How to solve this problem? I am using a shared server and was advised by the web host that I can't change php.ini to increase memory limit. 

[WZ_OZES]

Anyone has any idea? I was mucking around and did some searches over the forum and google. But no luck at all. 

Originally when I first time post this issue, the error happened when " - Updating magento/magento2-base (2.2.4 => 2.2.5): Downloading (50%)". But today when I tried again, it happened when " - Updating magento/magento2-base (2.2.4 => 2.2.5): Downloading (70%)". Not sure what makes the extra 20% download? 

I have checked using phpinfo() and my both local and master memory limit is 768M. Is this still not enough for upgrading to 2.2.5? 

Since this happened when downloading magento2 module, can I actually download it and upload it to the correct location? Can someone let me know where I can download it and which directory I should load the files to?