deleting files you dont need

[therock]

HI there,

i found that my touch is lagging when i open apps or just daily functions
is this normal
i dont have much installed on the phone mostly on my memory card
just like windows i was wondering if there is any programs that would defrag the hard drive.
And also there are files i dont use ...like pictures , sounds ..wall paper
I deleted some wallpapers when i select delete it just asks me that its a read file only...so i deleted like 5 wallpapers.
i tried to delete some other ones but said it was a system file so i did not.
Any one have any suggestions to speed up my phone or a least less lag and its is safe to delete files i dont need to free up some space

thanks to those the reply here