is it possible to upgrade a jammin rtr, to an x1 cr pro?

Yes but it will cost you an arm and a leg

or how about the x1cr to the new cr factory team kit?

The Jammin RTR is a particularly bad one to upgrade because it has a different chassis than the Pro kit. To do a full conversion, you will need:

CNC Chassis, CNC front/rear shock towers, CNC chassis braces, CNC z-brace, graphite upper plate, graphite radio tray, graphite diff plate, center and rear universals, CNC steering knuckles, CNC front upper/lower block (a or b), CNC rear tow in plate, lowered engine mount, CNC radio tray posts, CNC wing posts. I am not sure but I also think the shocks are upgraded as well.

Just did the math, using Nitrohouse's parts list, the parts come to 534.42 plus shipping.

Precisely.

i've been looking at the specs of the x1cr, and it seems to be from 8.5 to 10 centimeters shorter in length, and width.
is it really that small? all the other buggies have specs with a lenght and width larger than the one the x1cr has. am i right?

i can tell you one upgrade for the jammin....once you break the stock rear uprights replace them with kyosho 777 uprights...much stronger than the jammin ones