while formatting my memory card it has decreased to 8 megabytes. Originally it is 32 Gigabytes memory card. any idea on it, how to reformat as 32 gigabytes
Have you tried this? https://www.sdcard.org/downloads/formatter_4/
"I had the same problem, only 56MB would show. I used the program from this link. I formatted with the "FULL (overwrite)" option, which took a while, then the full SD card was available to me again. Thanks bredman"
I am going to assume that you are running on the Windows OS.
The raspbian operating system is a port of Debian Wheezy ( a Linux distro) , Linux uses the ext based file systems, which is not read windows as a result you will only see partitions that are either fat or NTFS based.
If you have Linux you can use gparted to detect and format the SD card to a file format of your choice or you can use the link ( https://www.sdcard.org/downloads/formatter_4/ )provided by Arita to format the SD card from windows.
Also you can verify the actual size of the SD card by right clicking my computer -> manage -> disk management. Here you will see your SD card with the actual size and the amount of free space etc.