Hi Roberta,
There is a easier option. Just on the header columns there is option configuration. 
before clicking on this, make sure you have arranged the columns in your required order. once inside this click on Administrator, then click on activate, then click on save. Now exit transaction and enter again, the columns should be in your required order.
Please note by doing this the rearrangement will be applicable for all users. If the changes is required only for selected users you have to maintain variant. and individual users has to make the variant as default for them.
Hope this clarifies. Award points if this helps.
Thanks
Vasudev