[6.3/Asterisk + Zaptel] Unloading module for upgrade?

[Gilles]

Hello

Since the Ports collection showed that there were more recent versions
of Asterisk and Zaptel, I tried to compile/install Zaptel, but it
fails, even after stopping Zaptel cleanly, and even after stopping
Asterisk itself:

=========
# kldstat
Id Refs Address    Size     Name
 1   14 0xc0400000 7a05b0   kernel
 3    5 0xc2caa000 32000    zaptel.ko
 4    1 0xc2ce0000 7000     qozap.ko
 5    1 0xc2ce7000 20000    tau32pci.ko
 6    1 0xc2d09000 5000     wcfxo.ko
 7    1 0xc2d0e000 a000     wcfxs.ko
 9    1 0xc2d26000 c000     wct4xxp.ko
=========
# /usr/local/etc/rc.d/zaptel stop
 zaptelkldunload: can't find file wcte12xp.ko: No such file or
directory
kldunload: can't find file wcte11xp.ko: No such file or directory
kldunload: can't find file wct1xxp.ko: No such file or directory
kldunload: can't find file wctdm24xxp.ko: No such file or directory
kldunload: can't find file wctdm.ko: No such file or directory
kldunload: can't unload file: Device busy
=========
# kldunload zaptel
kldunload: can't unload file: Device busy
=========
# kldunload qozap
# kldunload wcfxo
# kldunload wcfxs
# kldunload wct4xxp
# kldunload zaptel 
kldunload: can't unload file: Device busy
=========
# kldunload -f zaptel
kldunload: can't unload file: Device busy
=========
Dec 20 14:21:39 freebsd kernel: kldunload: attempt to unload file that
was loaded by the kernel
=========

What is the right way to upgrade Zaptel, without rebooting the host?

Thank you.