I updated my tom tom

Question

I updated my tom tom 910 from version 7.162 to 7.90. Since then it has become unstable. I have previous versions including 7.162 but the tom tom home software will not point to it to copy back to the device. However it will see it when you look at contents on computer. How can I load up the earlier version. I did not backup before the update but I do have previous backups from earlier vesions of Tomtom Home. Finally I've loaded v6.75 and it seems stable but too old for my latest map of UK.