push would create another head

[hamann.w at t-online.de]

Hi, sorry for beginner question. I copied an entire folder,
including the .hg directory, to my laptop and started working there.
Now, when I want to push back my changes (the proper way, this time),
mercuriasl suggests to either merge before pushing or force the push.
How / and what / could I merge? Is it safe to use force here?

Best regards
Wolfgang Hamann