There are differences between the SAT and ACT in terms of the test itself and the the registration process. Take a look at the tables here from collegeboard.org. to compare the two tests. Test dates for the SAT and ACT, as well as registration links are below.
-Step by step guide to registering for the SATs
-Step by step guide to claiming your fee waivers (available to economically eligible students)
-Self-guided online test prep is available through Khan Academy. Start by linking your PSAT scores to their website.
Power Point guide to linking scores to Khan Academy English)
Power Point guide to linking scores to Khan Academy (Spanish)
Video guide to linking scores to Khan Academy
Some schools are testing optional, which means that you can decide whether or not to submit test scores as a part of your application.
The schools that are test-optional are listed here. The table on the right from this report shows the growth in test optional colleges since 1969.
In addition to testing optional there are schools that do not require standardized test scores at all.
If you are applying to one or more test-optional schools, it is highly recommended you speak to Ms. Benzvi about whether or not it would make sense to submit your test scores for those schools.