My Bold has about 100MB application memory and 1GB device memory, how could I install from Appstore to the device memory? If not, is there any way to upgrade application memory?

Quick answer - You can't.
This questions gets asked a LOT (hint: use Search key) but there is no way to install apps to the device memory.

Wasn't RIM just so smart? They gave you 100MB of device memory, and a Micro SD card capability, both which can hold the same stuff. But Application memory - they haven't quite figured that out yet.

Blah blah blah. 8900 and 9700 have double the memory.
Aren't you so smart.