Hello Wisam
In general, the default values of the K metrics should not be changed. They are configured so that EIGRP will function correctly under the most common circumstances. However, if there is strange behaviour on your network or if you want to configure an elaborate routing behaviour, then K1 as well as the rest of the K values can be adjusted.
K1 can be set to anything between 0 and 256 (yes, 256, not 255) as can all of the K values. Specifically, K1 involves taking into account the minimum configured bandwidth between the router in question and the destination network. If K1 is 0 then the bandwidth is not taken into account. This would not be a good idea if you have links in your network with widely varying bandwidths. If K1 is greater than 1 then, the bandwidth will be taken into account much more than the rest of the K values.
You can find out more about this in Rene’s lesson on EIGRP K Values.
I hope this has been helpful!
Laz