How to delete Windows 7 files

hai, i am using win xp prof and win 7-32bit home in same sys as dual os in C and D, i plan to ugrade win 7 as Ultimate 64 bit, when i try to delete win7 files from windows Xp, it shows errors like accees deniend even i used some softwares like Unlocker 1.8, help me to solve my problem.... i want to delete all win7 folders. (i cant format... becoze its huge volume and having full of data)

advance thanks

You might try booting into Safe Mode and see if you can delete from there.

Just delete it when you install W7.