I am planning to upgrade my operating system Ubuntu 10.04 to Ubuntu 10.10. I want to know whether this upgrading will delete all the data or not?
As 10.10, and 11.04 even, are now end of life, while 11.10 will be in ~6 months, you should probably just upgrade direct to 12.04 instead.
An upgrade will only upgrade programs which are installed, though some old, unused, or no longer supported applications and libraries, may be removed during install; though you will have the option to keep them if so.
If you do an install from USB/CD-ROM/etc… then it will depend on how your system is currently partitioned, and whether you format or repartition any of it for the installation.
In either case, there is of course still risk of losing data, as there is no guarantee from Ubuntu that your hardware or power won't fail during the upgrade, or that some other external factors will not happen.
You should always back up any important and non-recoverable data.