Composer Update - Out of Memory

Hi,

I am trying to running composer update and ubuntu based server with 1GB RAM shows following error.

mmap() failed: [12] Cannot allocate memory
PHP Fatal error:  Out of memory (allocated 695214080) (tried to allocate 4096 bytes) in phar:///usr/local/bin/composer/src/Composer/DependencyResolver/RuleWatchGraph.php on line 52

Fatal error: Out of memory (allocated 695214080) (tried to allocate 4096 bytes) in phar:///usr/local/bin/composer/src/Composer/DependencyResolver/RuleWatchGraph.php on line 52

Command : free -h

root@Lumber-Tumber:/var/www/lumberdev# free -h
              total        used        free      shared  buff/cache   available
Mem:           992M        242M        639M         31M        109M        600M
Swap:            0B          0B          0B

Please advise. Thanks.