Try to clear your system incl. Metadata and try afterwards. It could be caused because of wrong metadata:

sudo yum clean all

Your droplet does not have enough memory to update. You need to stop some services or expand your droplet. I faced this issue when running a LEMP stack with wordpress, mysql was crashing and I couldn’t update after a day of being on. This was on a 512mb $5 droplet.

try

# yum --disableplugin=* <command>

and

# yum --setopt=deltarpm=0 <command>