I know that ANIMAL BIKES is not updated with the current version of the forge.
1. What version of Forge I need to install to use the ANIMAL BIKES?
2. Where to download?
3. How do I uninstall the old version of my Forge?
It requires Forge 3.1.3, you can get the client here: http://lexmanos.no-ip.org:8080/job/Forge/105/
. To uninstall your other version of Forge in the client just start with a clean minecraft.jar (delete and force update).
You'll also need the version of MCPC with the corresponding version of Forge, check the table on the wiki to see what version is included in what build. It may work with slightly newer builds but I had AnimalBikes 1.2.5v2 working for me on MCPC #91.