Can I use SSH to login remotely? How about SFTP?

Yes. Stellarmate does not use the default SSH port. Use port 5624 to login to StellarMate using your username and password.

ssh -p 5624 stellarmate@stellarmate.local

The same port should be used for SFTP (e.g. in FileZilla). You can perform remote update using the following command:

sudo apt-get update && sudo apt-get -y dist-upgrade