For the general case, accepting an answer is a privilege that is enjoyed only by the OP (original poster) of the question. If OP is a new user and presumably unaware of how accepting works, you may ask them (as you've done here); but if they decide not to accept any of the answers posted to their question, then nothing else can be done regarding it by the rest of us.
But particularly in this case, I don't think your answer actually solved OP's problem, they merely thanked you for your efforts. The comment should probably be read as
Hey, thanks for your efforts. I upgraded successfully.
I think so because I noticed OP also posted a self-answer explaining that switching to the main server as the download source solved the problem. I don't see anything mentioning this in your answer.
Update: Looks like OP accepted their own answer.