In order to fly an SEP on your CPL, you need to have a) a valid SEP rating, and b) a valid CPL.
Your SEP rating is valid for 2 years. If that expires, you will need to renew it. If it has expired by less than 5 years, you will need to do a test with an examiner, and the examiner can sign your license immediately after the test. If it has expired by more than 5 years, you will need to do a (slightly more thorough) test with an examiner, and then send the paperwork off to the CAA to have the new entry put into your license. In either case, there is no mandatory retraining, although I'd advise you to find a good school and do a bit of training.
Your CPL is valid for 5 years. If that expires, but you had a rating (any rating, your SEP rating will do) which has expired by less than 5 years, then you can pay the CAA to renew your CPL. If all your ratings (or your one and only rating) is expired by more than 5 years, you will need to renew it (as described above) before you can renew your license.
If you did the ATPL written exams (as oposed to the CPL written exams), then don't forget you only have 5 years from the date of your last exam to get your IR. There is no official way of "freezing" this, although I have heard of cases where the CAA have granted extensions due to extenuating circumstances (long term illness, etc).
All of this information is available in
LASORS - Section F1.6 for the SEP renewal, and section D9 for the CPL renewal.
Edit because I just checked your location, and I see you're not in the UK. The rules for a JAR license should be very similar in Sweden or anywhere else, but some of the details may vary slightly, so check with your own CAA.