If you don't have your recordings on MP3 then follow these instructions to rip them from your tapes (if you don't already know). If you have them on MP3 already then you can Upload here.
First of all, you need a cable to connect your tape/CD deck up to your PC if you don't already have one. In most cases, you will need an "RCA Phono to 3.5mm Stereo" lead which looks like this:
Tip: Some retailers may try to sell you 'super high quality' leads, a £3 lead will do just as well as a £20 one!
Connect the lead from your tape deck or hi-fi output to the line input of your PC.
You will need some recording software such as Audacity (new window)
You are now ready to record from the tape, simply play it and hit record in Audacity (or whatever you are using) and the level meters should start moving. When the tape reaches the end then stop the recording and export the file as an MP3 (File > Export as MP3). If you get an error then the chances are that it will want you to locate LAME (lame_enc.dll) which you should have downloaded with Audacity.
If you have problems exporting as MP3 then you can use a different format as long as the sound quality is reasonable.
Once you have the file saved, it's time to upload.