There are some TOS fixes which solve some problems like that. If you want to change your whole TOS, than you have to change the system - EPROMs.
THe newest TOS-version is the 2.06. To install this version you have to modify your ST's hardware. This is very difficult. If want a cheap solution for your problem, watch out for TOS 1.04. You'll find it in nearly every old ST built 1987 onwards.
If you want to created the EPROMs yourself, you'll find the Chip-images here: http://www.atari.co.uk/tos/