Q:

Update version of Process Builder and Pending Scheduled Actions

I would like to know what happen when I have some Scheduled Action for  version 1 of Process Builder A and I make some changes in the same Process Builder and activate version 2.

A:

You cannot do changes to the same process - you must clone it and then activate it to then replace the current process.

The other option is to Deactivate it and then create a new process, however, if you do this. 

After you deactivate a process, the scheduled actions continue as
  usual. If a deactivated process has pending scheduled actions and the
  record whose field the schedule is based on is changed, Salesforce
  recalculates the schedule for those actions.

You should probably go through Considerations for Scheduling Process Actions and update your post with your specific use case along any inconsistent behavior or the part in the documentation you don't understand based on your use case.

