How to resize ext3 image files

I have created an 200MB ext3 using the following commands. dd if=/dev/zero of=./system.img bs=1000000 count=200 mkfs.ext2 ./system.img tune2fs -j ./system.img How can I resize it to 50MB and 300MB? The problem is I have only some binaries in my system. They are : badblocks,e2fsck, mke2fs, mke2fs.bin, parted, resize2fs, tune2fs