deletion of existing org units and use of same numbers

dear guru's

namaste

almost this is the first day in sap for me. i found one problem. my client requirement is to assign external number ranges to org units. some how i managed with my client and i made them agreed for the assignment of internal no ranges.

now the problem is upto 50000197 nos already assigned to the various org units, jobs and positions as a trainl part by some other person. now i want to delete all those and i want to start the no from 50000001 onwards.

can anybody suggest me all the steps very clearly.

good support will be awarded.

thanx and regards

saathi