You can modify the schema of the remote database in the model, as follows.
To add tables to the remote database schema in the model, use the Create New Remote Tables dialog. The tables are added to the model and are mapped for synchronization. To open the Create New Remote Tables dialog in Model mode, choose File > New > Remote Tables.
If you want to add a table to the remote database and the table does not exist on the consolidated database, add the table on the consolidated database, run the Update Schema wizard, and then use the Create New Remote Tables dialog to add the table to the model. To open the Update Schema wizard in Model mode, from the File menu, choose Update Schema.
See Updating schemas in Model mode.
If you want to create new tables for an existing remote database, modify the remote database outside of the model and then use the Update Schema wizard to update the remote database schema in the model. You then need to map the new remote tables in the Mappings tab. See:
Model mode allows you to delete tables and columns from the remote database schema that is in the model. You can mark a remote table or column for deletion by right-clicking the row and choosing Delete. The remote table or column is deleted from the schema when you save the model. Deleting a remote table or column means that it will not be created in the remote database when you deploy to a new remote database.
You cannot delete a primary key.
You cannot delete tables or rows from the consolidated database in Model mode. To change the consolidated schema, modify the consolidated database outside of Model mode and then run the Update Schema wizard.