laptop makes it harder to upgrade the disc - but a usb external disk is a cheap and easy to install option for storage
at a guess you've filled the disk wirh either/or/and music video and photos ... all can be shifted to a usb disk
your main disk needs a minimum of 20% free - so you should aim at 50%
your other option is to sit down with a cake of CD/DVDs and do some serious backing up
stay away from windows, my programs and documents and settings - anything in my documents can be shifted ... but only delete files ... not folders - some of them ... my pictures ect are system folders
CCleader will do a good general cleanup ... just install and run (untick cookies if you have lots of memorised passwords)
http://www.ccleaner.com/download
IT IS FREE - it just asks for donations