Well, my first water change has been done... got one of those "vacuum pumps"to suck up all the muck in the gravel... I battled getting it going at first, but eventually worked like a charm... got rid of 50% of the water into my "fish bucket" (after taking Larry out and putting him aside in some of the tanks water) - he was not happy with me I might just add... and boy is he fast when I tried to catch him in the tank... I didn't want to freak him out, so I went as gently as possible... but this took a lot of time as well!
So, he was in my jug, set aside... just chilling out, and I started with the vacuum pump, eventually getting rid of 50% water, I put the ornaments, heater , thermometer inside this water ready to be cleaned. I washed the ornaments inside the old tank water, got rid of the "slime" (once again, I don't know all the terms), and put them back in the left over water in the tank.
I then broke the filter apart, and rinsed the filter "sponge"... man was that gross... (also in the old water from the tank) I then started adding my treated water to the tank... I finally got the exact liter capacity of my tank... it is 8 liters... :) is this big enough??? (don't know Gallons... sorry).
I let Larry wait for about 30 mins before I added him back into the tank... as I also wanted to ensure that the temp was just right, once it was back to normal (this took about 30 mins, as I said...) I added him back to the tank... HE SEEMED SO HAPPY! What I mean is, he was swimming, exploring his territory again, in the barrels around the plants, puffed up a bit to me, then swam away, all around the tank... I would like to think he was so excited!

I feel so relieved that I DID IT... and all worked out okay!
Please give me tips if you see anything that I might have done that you don't agree with...?
Also, when should I do a complete water change, like which entails ringing the gravel and everything, or should it just always be 50% water changes, and never really a complete change?
Thanks guys!!!