How to convert allegro to altium ？

   First you must have Cadence  setuped on you computer.
The DSN, and brd files can be imported into  Altium.  
then  you can edit your design in Altium.
If you mean  How to use Altium Designer, You can find a lot of  technique article in http://wiki.altium.com/display/PUB/Altium+Wiki

import wizard.

import wizard.

Do you come to install the B?