Several questions re: usage of stored data

hey,

i've been trying to delete stored data on my ipod touch. this is what i did:

tapped on settings icon>general>settings>usage

usage

storage

44.8 gb available 12.5 gb used

videos 10.8 gb

music 399 mb

facebook 81.4 mb

calendars & remi... 488 kb

mail 258 kb

messages 152 kb

now, i've deleted those messages and whatever is still in my mailbox [which is weird]. so, i can't use my finger>touch and slide left to delete. i don't get that option. so i'm wondering what else can i do?