Delinda is correct, changes to the data values in fields on the lead/contact/account records should be picked up in the next sync.
Changes to the picklist values in Salesforce will be picked up by Marketo. The admin will receive an automated email noting the change and any landing pages with that form will move into approved with draft status, according to this article:
https://community.marketo.com/MarketoArticle?id=kA050000000KzdqCAC. It was last modified in 2011, so forms 2.0 weren't around. Your forms may move to approved with draft and once approved, your landing pages will do the same.
Hope this helps!