Thank you for summary, SilverWarrior.
And what is the best way of cleaning the object instances from the memory and it's picture from the screen?
Now, I'm using arrays to store the instances and the FreeAndNil(); to delete the instances from the array, and after I use Canvas.Clear; to wipe the screen.
...
for i:=1 to numofenemies-1 do FreeAndNil(enemies[i]);
...
After all, it's works, but is this the only and best solution? Because in this case I have to give the maximum amount of enemies, shoots, etc. at the declaration of these arrays ( var enemies: array [1..100] of Tenemy; ), and I would like keep open the possibility to add new instances to the arrays, then redimensioning these arrays - if it's possible.