Hi
How can I increase download count by myself?
For example I have 5 device and I downloaded to them. After 1 day I uninstalled and installed again, does it count?
Is there any web site to exchange download. For example like website traffic exhange sites?
It does not count. Also, I think you need these devices to have different google accounts on them or it won’t count (but I’m not sure here, mb someone else could confirm).
You can try doing “reviews exchange” with other developers on “Promote Your Android App” subforum of MMWA, or Review Exchange of AndroidIncome.com 
Although I think you might do slightly better here on MMWA, cause I have 8 users online while here is 136 users online.
There were some networks where you could exchange banner impressions, like TapForTap etc, but I think it does not work.
Anyway, I guess you should focus on ASO - its free and might make huge difference for your downloads. For independent developers its the best way to get the traffic.