first i have a seperate drive in win7 by shriking the volume of 10 gb then i have installed ubuntu 11.04 via wubi and allocated a space of 5 gb from that 10 gb drive and this 5 gb is becoming less for me i want that the ubuntu take all the 10 gb space of the drive..so how can i resize the ubuntu space...
Wubi is designed so you can install without having to partition. Since you have a dedicated partition that you want to use entirely for Ubuntu, it would make more sense to do a normal dual boot install directly on the 10GB partition.
However, that doesn't answer your question... so here is how to resize the Wubi virtual disk:
You would need to do an "inplace" resize of the root.disk, which is possible if you boot an Ubuntu CD in live CD mode (Try without installing) and then use the following technique to resize. As mentioned in that post, you should backup the root.disk first (obviously to some place other than that 10GB volume).
I also think you will not be able to use the full remaining 5GB - probably you should leave a little space remaining, but I'm not sure how much.
PS the installation CD ISO Wubi used to install is hidden in the \ubuntu\install directory as .fuse_hidden000... and that takes 700MB so you could remove that to make some more space.