for some reason my connection speed dropped for 2MBps to 550KBps and is very unstable.
can someone please can give me some advice to fix this issue?thanks in advance

Have you tried turning off your router and restarting it, that usually can help sort out connection issues

Mine drops like that when I go over my weekly download limit but I'm guessing that really isn't an issue in Brazil unless you live out in the country like I do in the U.S.

Also storms can do it. I've got a blizzard here, how are you fairing?

yes,two times

Is it an unprotected WLAN in a city? :p

well,the weather here is unstable also,with rais every now and then no,it's a private connection

Mine is private too. It has something to do with my living in the middle of nowhere, I don't know tech stuff and it doesn't really matter because this isn't helping you.

I did a test of pluging directly into the modem and my speed went throu the roof.it's definetly my wi-fi

You get 2MBps? Wow, impressive. I'm lucky if I get a tenth of that.

Microwaves, other peoples routers and various other bits of tech can interfere with the wifi signal, so try moving your router and see if that helps at all.

I know the feeling (though lately its been about 500kbs)

This, and try changing the channel. If you have an Android phone, you can download Wifi Analyzer to check which channels are the least busy, then configure the router to use one of those.

Of course, the wifi shouldn't ever get down to those speeds (it should be at around 50 Mbit/s for 802.11g or even 150-200 Mbit/s for 802.11n), more likely is the internet connection being throttled for whatever reason.

If rebooting the computer and the router fails, the usual suspects would be some kind of processes running in the background. Might be malware or dead processes that still take up space. Just have a look at the process list (via Task Manager on Windows systems or via ps ax on Linux). And/or run a full virus scan.

If all that doesn't help, try contacting your provider. Sometimes the problem is on their side. (it was with me until they got around to fixing the line, which had a faulty connection somewhere).

as I said,when I plug directly into the modem,my speed goes way up,I'm sure that it's a reception problem