Sorry, I am confused.
Is an AirPort Time Capsule the same device that you mention on the first floor.....where you say that an "airport tower" is located?
Or, did you mean to say that you already have an AirPort Extreme or AirPort Express.....the device on the first floor where the "airport tower" is located......and you want to add an AirPort Time Capsule at another location to extend the network?
IF....the AirPort Time Capsule is the same device that you call an "airport tower" on the first floor.....and you need more wireless signal strength and coverage upstairs.....you can add an AirPort Extreme on the second floor.
The best way to connect the AirPort Extreme to the AirPort Time Capsule is via a wired Ethernet cable. Next best would be to use a pair of Ethernet over powerline adapters, but it might be possible to use wireless to connect the AirPort Extreme to the AirPort Time Capsule if you are willing to sacrifice some performance.
If you are saying that you already have an AirPort Extreme or AirPort Express......(the device on the first floor)......and you want to add an AirPort Time Capsule upstairs to provide more coverage, then the same things would apply. Connect the AirPort Time Capsule back to the AirPort downstairs using a wired Ethernet cable connection for best performance, use powerline adapters, or try using wireless if you are willing to give up some performance.
Please clarify things for us, so we will know how to proceed with the correct instructions.