[akhter]

I'll assume you mean the Alpine upgrade kit from BMW for those with base stereo (6 speakers/no amp in trunk).

There are 2 BMW alpine kits. One for pre 2010 builds that require splicing cables. and a newer kit for 2010+ models that require coding by the dealer. Not sure why, but probably because they switch the HU to output clean/un-eq'ed signal as the Hifi equipped cars.

there is a mounting place for the kit in the trunk under the board, behind the seat. the instructions that come with the kit will show it.

are you planning to do the upgrade yourself? you also have to take off the rear seats to route the new harness that taps into the connectors in each corner. atleast the new harness doesn't require splicing/cutting (compared to pre-2010 kit).

Here is the installation manual for the new kit (2010+) that require coding but no splicing.