Thats a very vague question. I believe you are asking if you can upgrade from Windows XP to Windows 7, yes? Well, if so you wouldn't be able to do a direct upgrade. It would require a clean install.
Though is Windows 7 is compatible with your computer? I'd need your computer's model number or Dell Service Tag (should be somewhere on the back of the case) to tell you.
My Computer
Computer Manufacturer/Model Number
Custom | Whitebox
OS
Windows 7 Ultimate, OS X 10.7, Ubuntu 11.04
CPU
Intel E6750 @ 3.80GHz
Motherboard
Gigabyte GA-EP45-UD3L (Revision 1.1)
Memory
2x2GB & 2x1GB (6GB) OCZ Reaper 1066MHz @ 1080MHz
Graphics Card(s)
EVGA nVidia GTX 260 896mb (216 Core) FTW Edition
Sound Card
Realtek ALC888
Monitor(s) Displays
21" VIZIO TV
Screen Resolution
1680x1050 @ 60Hz
Hard Drives
Western Digital WD6401AALS - 640GB
Hitachi HDP725016GLA380 - 160GB
PSU
Corsair 750W
Case
NZXT Nemesis Elite
Cooling
Thermaltake SpinQ
Keyboard
Logitech Wireless S520
Mouse
Logitech Wireless S520 - Microsoft Wireless Arc Mouse