Hello, Olielettef.
Thank you for visiting Apple Support Communities.
Sometimes a simple power cycle of the router can correct the issue that you are experiencing. However, the issue could be a little more complex. Wi-Fi routers need adjustments to settings periodically for optimized performance with the constant progression of wireless device technology. Below, I have included two articles. The first article will cover basic Wi-Fi troubleshooting regarding iOS device connection. The second article cover the recommended settings for current Wi-Fi access points.
iOS: Troubleshooting Wi-Fi networks and connections
http://support.apple.com/kb/ts1398
iOS and OS X: Recommended settings for Wi-Fi routers and access points
http://support.apple.com/kb/ht4199
Cheers,
Jason H.