Odd problem with Wireless connection

My internet is running slower when using wireless (with full bars). This started occurring like a week ago, before that the internet was running fine. I thought it was a problem with the internet but when I took it to my brother's room to plug in the wire, it was running smoothly. What can I do to fix this?

So you have tried changing wireless channels in your routers wireless set up page? Channel overlap is the number one reason for slow wireless, drop outs or rogue disconnections. Free software like Xirrus can help you see the wireless channels being used in your area so you can pick a better channel. Wi-Fi Inspector | Xirrus

You should also make sure to use WPA2 security with AES encryption. :)