Q:

Hyperledger-Composer. Modify the ledger via remote access

So far I have followed the hyperledger developer tutorial, but I have a couple of questions basically the same I pressume. Let us assume that I have running my application  as stated in the developer tutorial in machine A. 
The first question is: How can I modify the ledger in machine A from B when they are in the same network?.
The second is: How can I modify the ledger in machine A from B when they are in different networks?.

A:

The Composer Developer tutorial (and in fact all of the Compose tutorials) focus on the Composer aspects of developing and deploying a Business Network.  They do not focus much on the Fabric issues of multi-org and multi machine.  The Developer tutorial uses a very simple development Fabric of 1 Peer in 1 Organisation, and some automated scripts set this up for the developer to concentrate on the Model and the code.
For background on Hyperledger Fabric and experimentation with multi peer, multi org Fabrics I would suggest looking at the Fabric tutorials.
To get more of a view of Multi-Org from a Composer perspective I would suggest looking at the Composer Multi-Org Tutorial.  
Be aware that the above 2 references simulate multi-org Fabrics, but actually run on a single machine for simplicity.  There are other tutorials and blogs available in various places for running on multi-machine configurations e.g. https://www.skcript.com/svr/setting-up-a-blockchain-business-network-with-hyperledger-fabric-and-composer-running-in-multiple-physical-machine/

