You cannot if you want the pictures to be any good. Of course, I don't
know how well the film was stored and how good the pictures will be at
their best after all these years. But if you want it processed
correctly, you can send it to Rocky Mountain Film Laboratories:

http://www.rockymountainfilm.com/

They process everything old in the proper chemistry.   

Here is a clip from the website regarding old Ektachrome slide films
they process:

You have E4 (also E-4, E-3, E3, E-2 or E2) film which includes the
following types:
bullet    Kodak 2236 Infrared
bullet    Kodak Ektachrome, Ektachrome-X, or EHB
bullet    High Speed Ektachrome
bullet    Agfachrome
bullet    Fotomat
bullet    GAF 64 Slide
bullet    Fuji R55 R100
bullet    ORWOchrom UT18 or UT21 foreign film

Try them. But they are not quick and not inexpensive.

The emulsion will certainly come off the base if you process this film at
the 100 degrees of E6. E4 ran at 85 degrees. Of course you could try E6 at
85 degrees and process for a longer time to compensate, but you should clip
a small length to try it first. You could also process it as you would B&W
negative film. The color is probably going to be a waste anyway considering
the age of almost thirty years. Even B&W is a stretch. Just be sure to keep
it below 85 degrees.

john castronovo
tech photo & imaging