how can i remove the limit of itens in the feed?
actually there is no item limit per feed.
But I guess you mean the clean-up options that allow to delete old feed items automatically on shutdown.
Tools -> Options -> Feeds
and disable the option "Enable cleanup on shutdown" for general exclosure
or the single cleanup options separately..
But please be aware that the db size will encrease over the time and this might slow down QuiteRss.
That means you should clean-up the system manually from time to time..