Hi,
Assuming the you want change source system(new) to some data sources.
Before changing source system, first you need to implement the same data source at source system(new) and connect the new source system to bw system with help of basis team.
Once the data source was active in bw then no issue. it will work as you need.
Other wise you need to copy the from old source to new source system,
set connections from new source to bw system by using BDLS,WE20.
take basis team help.
Thanks