US Citizen visiting Schengen Countries for 3+ months

[immihelp]

Dear Sir/Madam

I am an US citizen, recently retired. I understand that an US citizen can visit Schengen countries upto 90 days with a valid passport. My question is if I want to extend my stay for some additional additional few weeks, what do I need to do.

I appreciate your advise in this regards.

Thanks.

[immihelp]

Get Schengen visa first.