I have the Rational Wildlife mod and I try to alter it so the wolves and bears (even plague) won′t attack me constantly in Solstheim. I lowered all their AI Fight to 0. I save the changes and start the game but they still attack me on sight. What is wrong?

Are you using a previous Save?
If so, be sure to Update your Save file with Wrye Mash.

Downloaded it but uncertain how to use it or even where to unzip it. Quickguide?

The http://wryemusings.com/Wrye%20Mash.html webpage has all the info needed.

If you are using the python version, I recommend installing the http://planetelderscrolls.gamespy.com/View.php?view=OblivionUtilities.Detail&id=44 so that you don't have to search for them yourself. (yes it works for Morrowind too, not just Oblivion)

There is also the http://www.gamesas.com/index.php?/topic/1106095-wrye-mash-stand-alone/

No substitute for reading the readme, but this is my basic "how to clean a save" thing:

Firstly, initial cleaning of your installed mods:
(1) On the Mods tab all mods should have a green checkbox.
(2) If any mods have a yellow checkbox, select them and then look for the Save button in the bottom right. Click that and the mod file will be updated and the error removed. The error just means that the mod was created with an earlier version of Morrowind to the one you're using. Saving in Mash will update this version info.
(3) If you have any mods with red checkboxes then you do not have a ESM file needed by that mod loaded. Check the mod's readme.
Secondly, cleaning your savegames:
(4) Onto the Saves tab, select the savegame you want to fix.
(5) When the savegame is selected the list in the bottom right will be populated with the mods currently associated with the savegame.
(6) Right click the column headers ("File" and "Num") above the list in the bottom right and choose Sync to Load List (this will change the mods associated with the savegame to match those currently selected on the Mods tab).
(7) Click Save
(8) Right click the savegame in the main list and choose Repair All.
(8a) Optionally, right click the savegame and choose Remove > Debris Cells.
(8b) Optionally, right click the savegame and choose Remove > Spawned Creatures.
(9) The checkbox for the save should now be purple.