Trying "yum -y update" Cannot allocate memory

Your VPS doesn't have enough memory available. You can see how much there is by running:

free -gh

The g shows how much memory is available in gigabytes and h puts in it human-readable format. You can use mh if you want to see it in megabytes.

In order for yum to work, you'll need to stop services to free up memory. You can see which processes are using what amount of memory by using the ps command.