Want to reinstal firmware in my usb pen drive

Hello,
I have one 8 GB USB Memory stick. Suddenly it shows only 1.9 GB now. I had formatted it and it happened after that. The same case had before with a Creative 4GB MP3 player.It showed a few MB only. I went to Creative website and downloaded firmware in my computer and updated the Mp3 . Then it worked perfectly as it did before.
In the same way I tried to correct this problem but I could not do so as the I dont know the correct brand name of this USB drive.I bought it from online shopping.there is nothing written on it. Please help me the way how I can regain the 8 GB capacity in it again. Thank you.