Process to update SDK for iOS?

I am getting a crash when trying to upload a file -- I have not update my app in a year.  What is the process to update the SDK?  I think I used Carthage to get the SDK installed before...

UPDATE: I tried "carthage update --platform iOS" in my project directory, and it looked like it was doing something.  Its said "Cloning dropbox-sdk-obj-c"  and then "Checking out dropbox-sdk-obj-c ay '3.0.11'", then gave this error message:

Error Domain=NSCocoaErrorDomain Code=260 "The file “ObjectiveDropboxOfficial.framework” couldn’t be opened because there is no such file." 

 UPDATE 2:  I see from my past posts here that I was using 3.0.11 because it was the last versiont to support iOS 8.  What is the oldest version of iOS supported by the newest Dropbox SDK (3.9.2) ?  

Note that when I updated my Cartfile to say "github "https://github.com/dropbox/dropbox-sdk-obj-c" ~> 3.9.2",  I now get this error message:

Fetching dropbox-sdk-obj-c
*** Checking out dropbox-sdk-obj-c at "3.9.2"
*** xcodebuild output can be found in /var/folders/rd/w5sm142d1sn3m4zq2djv3wnc0000gp/T/carthage-xcodebuild.oyTrL3.log
*** Building scheme "ObjectiveDropboxOfficial iOS" in ObjectiveDropboxOfficial.xcodeproj
2018-11-17 13:03:58.862 xcodebuild[8522:656734] [MT] iPhoneSupport: 📱<DVTiOSDevice (0x7f823d89cfd0), XXXXX, iPhone, 12.0.1 (16A404), f6bd8b1aa1c6e180effbaff25d2d9c999cbb2807> missing architecture for device
Failed to write to /...xxxxxx.../Carthage/Build/iOS/ObjectiveDropboxOfficial.framework: Error Domain=NSCocoaErrorDomain Code=260 "The file “ObjectiveDropboxOfficial.framework” couldn’t be opened because there is no such file." UserInfo={NSFilePath=/Users/xxx/Library/Developer/Xcode/DerivedData/ObjectiveDropboxOfficial-gglpwkwsxlwnfpftsoxrweyopqta/Build/Products/Release-iphoneos/ObjectiveDropboxOfficial.framework, NSUnderlyingError=0x7fd2cb128370 {Error Domain=NSPOSIXErrorDomain Code=2 "No such file or directory"}}

Thanks