W507 is the newest, released 2 months ago. If you are on W506, you are only one version behind, so you most likely just haven't been targeted since the updates are staggered. So best bet is to just wait and leave your receiver alone (no timers set to record either) every night at 2 AM (or whatever time the nightly reboot is set to on your box) until your box gets targeted (yes, it may seem like two months is too long but there may be a reason, maybe the update is buggy? its happened before).
If you really want to try to force the update anyway, there is a few ways to go about it. One is to force the receiver into recovery mode, this will make the receiver re-download software, but it takes a while and may or may not delete timers/settings/etc. The way to do this is holding power and arrow up on the receiver at the same time, and once it restarts releasing power but leaving arrow up pressed in. Keep holding until there is a screen with a blue background saying "Bootloader recovery" or something like that. Let that progress bar on the bottom fill up, and the receiver will reboot with whatever software it found on the satellite it connected to.
Few words of caution when doing this, if anything interrupts the update (being power or weather) there is a decent, not high, but decent chance something may break. Worst I've seen is a receiver bootlooping back into recovery mode over and over again. Also, and this is theoretical, I would not recommend doing this on a portable satellite dish, if you are an RV'er. Reason being is that I am not aware (if anybody has tried that would be great to know) if the receiver being in recovery mode will allow it to operate the portable, and for portable dish'es that can only see one satellite at a time, that may be an issue because I believe the software packages are only on specific satellites so you may get stuck if the dish cant rotate. Also, unless your portable is high end, odds are your signal strength is also low on a portable dish compared to a home one. And here is the best part: doing all this may amount to nothing, you may just not get W507 anyway without getting targeted for it.
TL;DR Just be patient, if you have an actual problem contact Dish/let us know.