If you have been using cPanel with your previous host then you need to create a full backup of your account on the old server, then transfer the backup file via FTP from the old server to your new account with Just Host. Please then inform us when this is done and we will restore your account from the backup provided by you.
If you were using another control panel then you need to download your website from the old server onto your local computer. Then you need to upload your files from your local computer into your Just Host account which can be done via FTP.
If you have issues please contact the support department and we will be more then happy to help you migrate your account over to our servers.