Packet Tracer

in CCNA & CCENT
I've attached Crossover cables between three routers, to the wrong interfaces.
How do I remove the cabling to reattach to the correct interfaces?
I keep trying but the cable won't go away and keeps giving me an error message that I can't reconnect, because the other end is a gigabit port and I want to connect the serial ports.
How do I remove the cabling to reattach to the correct interfaces?
I keep trying but the cable won't go away and keeps giving me an error message that I can't reconnect, because the other end is a gigabit port and I want to connect the serial ports.

Comments
I cannot compare the PT and GNS3 courses because I purchased my study material from friends who teach for a living. PT is sufficient for CCNA R&S but GNS3 is recommended for CCNA Sec, CCNP and higher exams.
My suggestion for CCNA is build a foundation with whatever method that suits you best (let it be aural, video or book) and then utilize Boson to test your knowledge.
Foundation:
Subnetting - know it and know it well
Decimal to/from binary - know how to convert from one to the other.
Binary to/from hex - know how to convert from one to the other.
MAC address - knowing hex will help a lot. Know the basics of mac address.
IPV6 - know the basics: unicast, multicast, loopback, differences between IPV4 and IPV6.
Routing - understand the differences
OSPF/OSPFV3 - know how to configure and troubleshoot
EIGRP - know how to configure and troubleshoot
RIP/RIPV2 - know how to configure and troubleshoot
BGP/iBGP - know the differences.