First, find the location of your installed redis-server instance before updating. In my case, it was in /usr/local/bin/, but it might also be in /usr/bin/. If it's not here, you can type which redis-server to find the location. Next, download the redis tar file from https://redis.io/download, then install it from the directory it downloaded to: cd Downloads
wget http://download.redis.io/releases/redis-X.Y.Z.tar.gztar xzf redis-X.Y.Z.tar.gz
cd redis-X.Y.Z
make
make test