Open um.dat with a hex editor
change to the following (ensure that exists 41 64 6d 69 6e)
0000080 55 55 bc 7f 41 64 6d 69 6e 00 00 00 00 00 00 00
0000090 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00000A0 00 00 00 00 90 6e 00 00 a8 01 00 00 00 00 00 00
41 64 6d 69 6e = Admin