First step
Login to device as an administrator user.

Second step
Select Network tab.

Third step
Change Configuration mode from Simple to Advanced.

Click Change button.

Fourth step
Add desired VLAN to LAN and WLAN interfaces.

Click Change button.

Fifth step
Create new bridge and add earlier defined VLAN interfaces to it.

Click Change button.

Sixth step
Change Management Interface to earlier created bridge and adjust network settings.

Click Change button.

Seventh step
Apply or test changes on the top of the page.

Ubiquiti Beta Program provides access to beta versions of AirOS releases.
To access it perform following steps:
First Step
Join Ubiquiti Networks Forum.

Second step
Sign up to Ubiquiti Beta Program.

Third step
Access AirOS V Beta Discussion.
The path is Ubiquiti Networks Forum > Ubiquiti Product Forum > Ubiquiti AirMax, AirOS V and M Series Products > AirOS V Beta Discussion

Using firmware version v5.3.3 there is no way to set management vlan using browser, but it can be easily set using SSH in couple of steps as described below. More information can be found at Ubiquiti Networks Forum.
Edit rc.poststart script:
# vi /etc/persistent/rc.poststart
For example to set IP address 10.1.2.3 on vlan 123 and remove general IP address set in browser you can use such commands:
vconfig add br0 123
ifconfig br0.123 10.1.2.3 netmask 255.255.255.0 up
ifconfig br0 0.0.0.0
Make rc.poststart file executable and check changes:
XM.v5.3.3# chmod +x /etc/persistent/rc.poststart
XM.v5.3.3# /etc/persistent/rc.poststart
Store changes to flash if everything works as expected:
XM.v5.3.3# cfgmtd -w -p /etc/
Found Backup1 on[1] ...
Found Active on[2] ...
Storing Active[1] ... [%100]
Active->Backup[2] ... [%100]
Reboot device:
XM.v5.3.3# reboot
ifconfig output:
XM.v5.3.3# ifconfig
ath0 Link encap:Ethernet HWaddr 00:27:22:11:11:11
UP BROADCAST RUNNING PROMISC ALLMULTI MULTICAST MTU:1500 Metric:1
RX packets:381 errors:0 dropped:0 overruns:0 frame:0
TX packets:2299 errors:0 dropped:62 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:47931 (46.8 KiB) TX bytes:222735 (217.5 KiB)
br0 Link encap:Ethernet HWaddr 00:27:22:11:11:11
UP BROADCAST RUNNING ALLMULTI MULTICAST MTU:1500 Metric:1
RX packets:2086 errors:0 dropped:0 overruns:0 frame:0
TX packets:181 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:209570 (204.6 KiB) TX bytes:69112 (67.4 KiB)
br0.101 Link encap:Ethernet HWaddr 00:27:22:11:11:11
inet addr:10.1.2.3 Bcast:10.1.2.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:201 errors:0 dropped:0 overruns:0 frame:0
TX packets:181 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:23315 (22.7 KiB) TX bytes:69112 (67.4 KiB)
eth0 Link encap:Ethernet HWaddr 00:27:22:22:22:22
UP BROADCAST RUNNING PROMISC ALLMULTI MULTICAST MTU:1500 Metric:1
RX packets:2586 errors:0 dropped:0 overruns:0 frame:0
TX packets:563 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:500
RX bytes:295818 (288.8 KiB) TX bytes:116621 (113.8 KiB)
eth1 Link encap:Ethernet HWaddr 02:27:22:22:22:22
UP BROADCAST PROMISC ALLMULTI MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:500
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
wifi0 Link encap:Ethernet HWaddr 00:27:22:11:11:11
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:500
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
Interrupt:48 Memory:b0000000-b0010000
Update
Since AirOS 5.5 everything can be done using browser.
Check this post