You don't, generally.
If your app uses SQLlite, then it's a single user database system.
If you need to integrate that info with a multiuser SQL server DB, then exactly what to do depends on how your app is being used.
If it's always on the LAN and can access the SQl Server instance, then change you app to use SQLConnection, SQLCommand, etc. objects instead of the SqLite eqivilents (SQLiteConnection, SQLiteCommand, etc.). Pretty much, it'll work unchanged, provided you designed the app right in the first place.
If it isn't, then it's a seriously major job. Start by reading up on Database replication:
MSDN[
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