Hi Begoña!
Don't worry about your English, it's perfectly understandable.
There's a topic in the wiki about this:
English /
SpanishYou'll find a lots of useful tipps there.
I suggest to lower the values for max. sources for a file (hard limit) and max. connections to the default values again, there's the risk of 'overstraining'. (e.g. Routers will freeze/restart) Your bandwith limits seem fine to me as well.
Slot allocation will influence the aimed upload speed to each client and therefore the number of uploads. 10KB Upload total/2KB Upload per client =5 upload slots. Seems well too.
Your problems are probably the points 2-4 in the "network's fault"-section of the wiki page. Choose popular files in favor of impopular ones and wait. The longer aMule's running, the better for your speed. The best case is 24hours daily, 7days a week.
Hope I could help you a bit.