Can I install a 240GB hard drive in this tablet?

You're going to want to open up the tablet like in the various guides for this device. Inside you'll have to find the 128gb MSATA SSD inside. You may need to do a little digging since I don't own this device or are familliar with it's internals. But when you do you find the SSD you'll want to take it out and insert the new one in it's place the same way you pulled out the original, but in reverse. Make sure the replacement is also an MSATA SSD because of the internal design of the tablet you can only fit the same type of SSD.