one line answers, ok, lets put yourname to shame
OK, lets take a few asumptions.
1: You home dir is "/home/user/"
2: You installed your eggdrop in "/home/user/eggdrop/"
First step, kill the previous bot, this will prevent problems.
Download eggdrop1.6.6.tar.gz from the ftp site, ftp.eggheads.org, under the directory "/pub/eggdrop/source/1.6/" into your home directory.
Decompress and unpackage the the file, using "tar zxf eggdrop1.6.6.tar.gz".
Next, changing into the newly created directory "cd eggdrop1.6"
You now configure and compile the eggdrop as normal.
At the "make install" stage, you basicaly, make it install over the top of the previous installtion with "make install DEST=~/eggdrop"
You will now have new binaries, modules, config files and documentation installed in the eggdrop directory.
You should now go through the doc/updates1.6 file, and chack what config file settings might have changed, added or removed, and make sure your config file is changed acordingly.
In the eggdrop directory, there will be a file called eggdrop1.6.6, and a directory called modules1.6.6. These are the actual locations of the files. eggdrop, and modules are just links to these. As such, there will be a file eggdrop1.6.4 and a directory modules1.6.4. You may delete these to free some space.
You may now restart your bot as normal.