From singular to plural substantives words in German...
In German I know that the plural of substantives change at the end of the word, for example: die Lampe-die Lampen in which there is an “n” at the end of the singular word to make it plural; der Tisch-die Tische in which there is an “e” in the plural; but how can I know how would be the end-change or extra letter of singular substantives when make it plural? Is there a rule I can follow to know it? Or should I just memorize it?

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Die meisten Nomen bilden ihre Pluralform mit e(n), aber es lässt sich keine allgemeingültige Regel bestimmen. Also am besten wäre es, sie gleich mitzulernen. 
Hier findet man eine gute Übersicht:
http://www.mein-deutschbuch.de/lernen.php?menu_id=53

Answer

There are some rules ... and more exceptions (again: some are already mentioned above)
rule "der"
"e" at the end of the word and the German Umlaut on the vowel. 
der Baum - die Bäume
der Schrank - die Schränke

exception:
a noun is ending on -el, -en, -er => no change at all
der Esel - die Esel
der Hamster - die Hamster
das Mädchen - die Mädchen

exception: der Apfel - die Äpfel, der Bruder - die Brüder, der Laden - die Läden, der Vater - die Väter

and some more exceptions ......

rule "die"
noun in plural comes with "en" (except noun is ending on "r" or there already is en "e" at the end)
die Frau - die Frauen, die Katze - die Katzen
die Dame - die Damen
die Schwester - die Schwestern

nouns ending on -nis: +se
die Erkenntnis - die Erkenntnisse

rule "das"
no change in plural with nouns ending on -el, -en, -er, -chen, -lein

general guideline: nouns ending on a vowel, add an 's'
das Radio - die Radios
das Kino - die Kinos

Answer

Hello, 

a) In most cases , au changes to äu: der Baum - die Bäume; der Traum /der Raum - die Träume - die Räume

b) a often changes to a-umlaut: Kamm - Kämme, Mann - Männer, Ball - Bälle

c)  Likewise the letter o often becomes o-umlaut: Lohn-Löhne, Sohn-Söhne, das Loch - die Löcher


d) The plural ending -er is used with male or neuter nouns: das Haus - Häuser; der Mann - Männer; das Land - Länder 

This should be enough for a start. Some of the forms have just to be learned . Here is a website for further information: 

deutschseite.de

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There are a large number of rules, and most rules have lists of exceptions. Confused? You should be. I'm afraid you'll have to learn them one by one.
I can't recommend one website over another for learning this stuff. I'm afraid you'll have to Google an explore an number of them before you get the gist here. Don't be put off so quickly. It's going to take you a few months before you crack this one.