Hi there, welcome to the forum.
I always thought that there was no danger with aluminum wire as long as all the connectors are designed for aluminum wire. If someone has changed switches or outlets and used standard parts(designed for copper wire)... then there can be a problem with the connectors coming loose, overheating and causing serious problems.
Here is a website with info and links to tons of other sites...
http://www.inspect-ny.com/aluminum.htm
If you are changing to copper then you have to replace all the wire and all the outlets/switches/connectors. Or use proper 'pigtail' connectors to convert to copper just before the switch or outlet.
As with any electrical work your requirement for using a licensed electrician depends on your local codes and/or your confidence in doing the work yourself.
I would recommend continuing your research and talking to local electricians for quotes and their recommendations.
Best of luck, Jim
'Just a handyman trying to help'