Select a local variable (or a function argument), press Ctrl+Shift+R or choose Rename Symbol. It's background will become red, and if edited, all instances will be renamed.

It used to work in one of the previous prereleases. Now, when I do it it writes backwards.

e.g. variable name is test, and I want to change it to newvar. I mark it and choose rename symbol, then I write newvar, the result is testravwen. It doesn't erase the previous name, and it appends always on the same location, causing it to be written backwards.