If you need to upload files from your windows machine to a Linkit 7688 Duo or Arduino yun, most likely your sftp program will not wot work. Please use winSCP for this purpose. You can download it from https://winscp.net/download/ Use the SCP protocol to connect to the linkit/arduino yun.
Sometimes their is an application missing in a new openwrt release which was present in an older version. Luckily you can still download the older packages. You only need to find the right architecture to now where to download from.
https://downloads.openwrt.org/ choice your release, eg. barrier_breaker/14.07/ and then the Linkit MPU architecture ramips/mt7620a/packages/
You can download it via wget and then opkg install [filename].