Ok Ruben Miranda, I am planning to put in a new liner in my existing pond sometime this week or next. So just to clarify from your ideas, I will be doing this:
Drain the water first by scooping water with a bucket and putting it in a separate barrel, and when the water becomes too shallow, I will start using the pond pump to drain the rest of the water into the barrel. Then I will get a disposable towel and wipe all the sludge and dirt/debris from the bottom of the pond. And while I am doing this, I will put the 4 fish in the smaller pond right next to it since that doesn't have any problems leaking(as you can see from my pic), and I will also put in my water lettuce into that smaller pond. Then I will wash the liner with the hose to just get some of the dust and stuff off. Then after I finish getting all the water into the barrel, I will now add the new liner into my existing pond. Then put those flat rocks on the edges of the pond to cover the liner. Then pour all the water from the barrel into the pond with the new liner installed in. Then return the fish and water lettuce into their original pond! Then I'll add my beneficial bacterias for cleaning. How does that sound?
Also I don't have a filter and never have used one all the 12 years we've had this pond, do I really need one? Also can I add pond rocks in my pond right away after I put my liner in? Do I have to wash the rocks off for dirt before that?