How do neurons form new connections in brain plasticity?
I haven't read anything particularly about dendrites being reshaped, though I would expect them to be as flexible as other parts of the cells.

The more commonly discussed topic (in my literary experience) is reshaping of the axon's branches before forming synaptic terminals. These branches are not fixed even in adults - neurons can grow new and retract old branches, attaching (synapsing) to other cells in new places and removing old connections (see Wikipedia: Synaptogenesis).

Additionally to this actual change in the number of synapses, individual synapses can be regulated in their signal strength by adjusting the number of neurotransmitter receptors in the postsynaptic membrane (Gerrow&amp;Triller, 2010, also see Wikipedia: Synaptic plasticity)