For maintain number range of SL you can find below customizing:
SPRO->Special Purpose Ledger->Actual Posting->Number Ranges->Maintain Local Number Ranges
SPRO ->Special Purpose Ledger->Planning->Plan Settings->Number Ranges->Maintain Local Number Ranges
There is little confuse for above two transactions for you can maintain Number Ranges both: plan and actual data.
The number range is distinguished by the document type.
The actual data usually have the number range ‘01’ assigned whereas the plan data use the number range ‘02’ (see transaction GCBX and GCBA).