It's most likely file permissions. I assume you're logging in as ec2-user with a certificate. That user won't have permission to write files to where you're trying.
You can add ec-2 user to the group that has permission to write to those folders and files, or you can create a new user that has appropriate permissions.
The way I did it was I create a new user (eg bob), then added bob to the www-data group. I made sure files and folders were owned by the www-data group
I've got an article on this here. They key parts are below, see the link for a bit more explanation.
sudo su
sudo useradd fred
passwd fred
su fred
ssh-keygen -f fred-t rsa
mkdir .ssh
touch .ssh/authorized_keys
chmod go-w ~/
chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys
cat fred.pub >> /home/fred/.ssh/authorized_keys
vi /etc/ssh/sshd_config
PasswordAuthentication no
AllowUsers ec2-user fred
You'll need to give fred access to those files
groupadd www-data
chown -R fred:www-data /var/www
# Change webroot permissions
find /var/www -type d -exec chmod 755 {} \;
find /var/www -type f -exec chmod 644 {} \;
# Wordpress specific
find /var/www/wp-content/uploads -type f -exec chmod 664 {} \;
find /var/www/wp-content/plugins -type f -exec chmod 664 {} \;
find /var/www/wp-content/themes -type f -exec chmod 644 {} \;
chmod 440 /var/www/wp-config.php
chmod -R g+s /var/www/
In either case, now you know what the problem is, you can Google things like permissions, adding users to groups, creating groups, etc. I didn't know anything about this stuff 18 months ago, I had a developer background, I learned by doing, reading tutorials, and experimenting. Keep backups.
