Does anybody know is there is a software release to increase the 4402 from 25 to 50 AP's
You won't love this answer but, the number of supported AP's on a WLC is based on the Hardware configuration and cannot be changed. You will need to purchase a second WLC. The upside is you will be able to add some redundancy to your deployment :)
\\The limitation on the number of supported access points is based on the hardware that you have. The 4402 WLC with two gigabit Ethernet ports comes in configurations that support 12, 25, and 50 access points. The 4404 WLC with four gigabit Ethernet ports supports 100 access points.
4400 Series WLAN Controller for up to 12 Cisco access points
4400 Series WLAN Controller for up to 25 Cisco access points
4400 Series WLAN Controller for up to 50 Cisco access points
4400 Series WLAN Controller for up to 100 Cisco access points
Hope this helps!