Should I upgrade my towers?

$4k used speakers will put you in another world sonically.  Absolutely upgrade!  Since you're relatively new to this, if you buy used I'd try to go with something that's not extreme one way or the other and that tends to shoot straight down the audio fairway.  Some brands that many people like and rarely get negative comments (off the top of my head) are Joseph Audio, ProAc, and Silverline.  There are a couple pairs of Joseph Audio Profiles (originally $7k/pr.) for sale here now in your price range, and I'd be shocked if they don't absolutely blow you away.  If they don't you can likely sell them for little or no loss.  

Couple last thoughts -- the Profiles (and many good speakers) appreciate some space between them and the rear wall to sound more balanced and image properly.  Also, these speakers (and virtually all others recommended here) will greatly reward you with a good separate stereo amp and preamp rather than a receiver -- just a thought for down the road a bit, and something to look forward to actually.  Best of luck!

Focal Aria 936 would be great in your price range, but there are hundreds of speakers out there to research and audition.  The problem with Focal is that there are so few brick and mortar shops that have them for audition.  Paradigm and Klipsch are much easier to find.  If your Best Buy has a Magnolia in it, then they will have some nice speakers to check out.  Revel Performa 206 is also another nice one to check out.  Monitor Audio, B&W, KEF, and Golden Ear are other companies to check out.

Once again, you really have to listen to them.
Since you don't have a local dealer, maybe you can try manufacturers who offer a trial period.
I know Zu, Magnepan, and Tekton offer trials. You just have to pay for return shipping.
I haven't heard Focal's, and I haven't heard Klipsch in decades. Though in my opinion, I think you could do better.
Sensitivity only relates to how easy they will be powered. How they sound to you is another matter.
B

Any suggestions? I read the Focals are high in sensitivity... maybe a newer version of a Klipsch?

You can get some great speakers for 4K. Need to be careful what you are buying with an avr to match well. Should be efficient with not a lot of big impedance dips at or below 4 ohms. 

gdnrbob... thanks for the suggestions, I will look into them. As for dealers, only BestBuy around me. So, it will be a blind buy. 

Freediver... that’s a great suggestion, thank you too!

IMO the very first thing you should do is go listen to live unamplified music!!!Go to a small jazz or blues club,the local symphony,a downtown streetcorner,even bookstores have open mic night.Pick up a guitar.Strum it,even if you can’t play it you will know what the basic sound(tone)is.Like rock and roll or electric blues,go hang out in a Guitar Center on a holiday weekend.I am constantly amazed at the people I hear playing around GC...You need a baseline for what music is supposed to sound like...

Are you near dealers?
As you said you 'know nothing about sound', it would behoove you to go listening to as many speakers as you can. Eventually, you will find the ones that work with your ears.
As far as brands go:
Vandersteen, Magnepan, ProAc, Zu, would be my choices. Others will give you even more choices.
Be prepared to start changing the rest of the system, once you hear how good the new speakers sound.
B

Thanks, James... would you mind recommending a few brands to check out?