No, IMO swapping the antenna will not help.
Also, a wireless extender is not the best option, instead go for a remote access point using either of them upstairs. The real issue is getting a CAT5 cable up from the main router to the top floor where you would place the AP.
Hi, no not swapping, adding,soldering together like two 5dbi antenna & cat5 is a big problem because i use tp link modem right now and connect it to tplink router coz the asus has only Rj-12 input not Rj-45 and the modem in it dont work so i dnt use it!!