Sometimes just clicking..? No crank no start..

Hello! I've got a K12 2005 1.2 model. A day ago, it suddenly wouldnt start after an hour of driving. I can only hear that the relays are clicking, but thats it. I had to push it in order to start (its a manual). After this, I went home and tried to start the car again, and it worked like nothing ever happen. However, same thing happen today. After a drive to the store, it did the same thing, only clicking sounds from the relays again and I once again had to push the car to run.. Lights and things are working, the relays do click, so all I can assume is that the starter is done? If you guys think so too, is it difficult to change yourself?
Battery or alternator, clicking is usually the starter trying to start, and then pulling the battery right down to the point it releases the solenoid.

Check the voltage with the car off, then with engine running to see if it's the alternator or not.
Post back the voltages.