Ram you need to get the correct ram for the board go click here yes the clips at both ends are what holds it in. just pull the clip away then when fitting just press ram in untill the clips go back on there own.
Yes the Hard Drive is very easy to fit, if you have just one hard drive and a CD or DVD they may be connected to the same Data Cable. So you would need extra cable a 80 wire Ribbon and the Drive should be set to Slave if it is being connected to same cable as other drive.
PS there may be a limit on the size of drive that the BIOS can see and use.
You may need a bigger PSU as fitting a new hard drive will put more load on the one that's in and it just may blow and do some damage
For the Fan use a small art paint brush and compressed air