A Wireless Local Area Network (WLAN) is a type of Local Area Network (LAN) that uses high frequency radio waves rather than wires to communicate and transmit data. It is a flexible data communication system implemented as an extension to or as an alternative for, a wired LAN. It provides large companies the option to connect the current wired networks to the wireless network without any problems and gives user the option to use any kind of applications regardless of its source or vendors. As data sharing is sometimes slow or worst slowness due to the performance of the WLAN which is a key factor in spreading and usage of such technologies. Hence it is necessary to identify the quality of the wireless connection and how to improve the communication through the WLAN. Therefore, in this paper, Evaluating and Improving Wireless LANs Performance has been proposed to address mains parameters as Wireless LAN performance indicators and then to propose some methods to improve the performance of WLAN connection via OPNET Modeler 9.1., an advanced network simulator.