If you don't know how, don't upgrade the CPU. Even if you knew what you are doing:
1. It could be soldered on making the task impossible.
2. It's not like a desktop. There is a lot of disassembly and you'd have to make sure your bios supports it.
3. Even if you are willing to go through all that, mobile processors are hard to find and expensive.
The ram and hard drive are easy. Your computer uses DDR2 ram I believe. To find out the maximum supported ram look up your specific model on the compaq site. You will be purchasing SO-DIMM. The hard drive will be the same for all computers. Check the site to see if you have a SATA drive or IDE drive and purchase the appropriate 2.5" drive. You can upgrade the speed (RPM) and/or the capacity.
You will have to look up the service manual for your computer on their site. That will have instructions for assembly, disassembly and component replacement specific to your computer.