If you want to have the latest firmware, you must install it. I suppose you know that you must execute the update app to install it. It doesn't magically update itself by copying the opk to the console.
Download the 2014-05-05 OPK, transfer it to the console, and then execute it and follow the instructions on screen to install it. After installing it, delete the opk. Then download the 2014-08-20 OPK, transfer it, execute it, and after installing, delete it.
It's a simple procedure.
Note that the icons are the same for all update apps, so you may accidentally execute the same update twice, thinking it's the newer one. That's why i advise to transfer the updates one by one and then delete them, so there is no possibility of confusion.