  An edge labeling of a connected graph $G = (V, E)$ is said to be local
antimagic if it is a bijection $f:E \to\{1,\ldots ,|E|\}$ such that for any
pair of adjacent vertices $x$ and $y$, $f^+(x)\not= f^+(y)$, where the induced
vertex label $f^+(x)= \sum f(e)$, with $e$ ranging over all the edges incident
to $x$. The local antimagic chromatic number of $G$, denoted by $\chi_{la}(G)$,
is the minimum number of distinct induced vertex labels over all local
antimagic labelings of $G$. In this paper, several sufficient conditions for
$\chi_{la}(H)\le \chi_{la}(G)$ are obtained, where $H$ is obtained from $G$
with a certain edge deleted or added. We then determined the exact value of the
local antimagic chromatic number of many cycle related join graphs.
