Any reason you want to do that?If I put them side ways will still work?
And also I have it in pair can I combine 2 of them side by side In the centre and use them as one speaker
This is the model Klipsch R41M 50-Watt Bookshelf Speaker
I mean, as stated, you can do anything you want, buuuut if you don't have a bi-amped center channel on your AVR (as stated) you will run into issues with wiring where you either halve the resistance or double it; two 8ohm speakers wired together would either be a 4ohm load (not the worst, but I would not do this unless you know for a fact the speakers and your avr can handle it [most likely not] or 16ohms (probably not going to work, but if it did, it likely would not be loud enough).
You can put one sideways no problem, so I would just stick with that. If you want both there (for aesthetic purposes), I'd just leave it not hooked up. Sure, doubling the speaker could make it louder (at the same AVR level), but you can also just turn up the AVR more/raise the center channel level. If you are concerned about volume, I'd just look for a more sensitive speaker (increased sensitivity = less power to get a certain volume; most klipsches are pretty sensitive, so you can always test it to see if just one is loud enough).