You don't need a conversion tool.
You just need a copy of Ver10 or VerXI, open the 8.5 report(s) into either version and save the file.
This "upgrades" the 8.5 rpt file to whichever version you have opened and saved the rpt file from.
Note you will no longer be able to open the "upgraded" rpt file in 8.5 after this process has been performed.
FYI, Ver 9, 10 and XI can open each others rpt files and run them. Ver 8.5 cannot.