Comment 200 for bug 185311

I want to change the latest edition of libx11-6 with the "non xcb" version (I've the problem of jhyder79 in Pro/Engineer with very slowy slid-up windows). I've downloaded libx11-6_1.1.3-1ubuntu2~noxcb_i386.deb but I don't understand how to make the change with my actual libx11-6 (error: a later version is already installed). I've Intrepid Ibex 8.10 with pre-released and unsupported updates activated.