The option on the top is a large green + sign.
To the left of your mods, should be a short menu of options. This will look up the mod on Nexus Mods to see if it has been changed. When right clicking on a single mod you can select "Check for Update". posted in Skyrim Mod Talk: It's been a while since I've played Skyrim and I. of 3 - How to update mods from Nexus Mod Manager? Click on the version number, download latest version, right click installed mod and select "uninstall and delete" (or something like that), activate new version.