updating packages?

I am trying to update the packages that I have installed but I get the following warning messages:

package 'tseries' successfully unpacked and MD5 sums checked
Warning: cannot remove prior installation of package 'tseries'
bundle 'forecasting' successfully unpacked and MD5 sums checked
Warning: cannot remove prior installation of package 'forecast'

What does that mean? How can I update these packages?

Thank you.

Kevin