Lightroom catalog size issue

[Flash and Flicker]

I am using iMac which have 256GB disk and using lighrrom exensively. Catalog back was on the same disk. Now I selected an external disk for catlog back to reduce risk and save my disk speace. I see there is on file Lightroom Catlog-v13-3 Previews.Irdata is 120GB. This is consuming my space. 
I have two question.

1. Since I seelcted  catlog backup folder on external disk, do I cleanup/delete earlier catlog file from my IMac disk?
2. How can I reduce size of file Lightroom Catlog-v13-3 Previews.Irdata?

Thnaks in advance!

[AxelMatt]

1. Since I seelcted  catlog backup folder on external disk, do I cleanup/delete earlier catlog file from my IMac disk?

By @Flash and Flicker

During the installation of major update the catalog has to updated to the new structure. If this has worked without anyproblems and you have the approprite backups you can delete the older catalog files.

2. How can I reduce size of file Lightroom Catlog-v13-3 Previews.Irdata?

Thnaks in advance!

By @Flash and Flicker

Check your settings on the Previews tab in the Catalog settings dialog. In a first step you can set the automatic discarding  of the 1:1 previews to "After 30 days" (or to "One Week"). The other alternative you can limited the cache size for example to  100GB.

You can also reduce the quality of the previews in the same dialog.

More informations you'll fnd here: How to create and manage catalogs in Photoshop Lightroom Classic (adobe.com)

[JohanElzenga]

If you look at the screenshot in the previous message, you'll see that there is a new option: Limit Preview Cache Size. This is new in lrc 14 and that is exactly what would be ideal for you, because that will be much more effective than just deleting 1:1 previews. Check this option and fill in a value that is reasonable for you. Do remember that the bigger the cache, the less preview-rebuilding Lightroom will have to do when you scroll through older images, so use a sensible size.

[Flash and Flicker]

Thnak you for your response. Unfortunetly I can't see file size limit box in my Lightroom classic.  Eariler I set a backup path on different place but now it's started doing on same disk and again setup a backup folder is not visible any where.

[JohanElzenga]

Looks like you are not using Lightroom Classic 14 yet.

[Flash and Flicker]

Updaate it and now I can see this option. Thank you!!

[KR Seals]

Now that you are using LrC 14, one of the nice new features is the ability to "Rename the Catalog". You can find that under the File menu. 

I suggest renaming with something that includes the Version 14 wording. There is a checkbox to rename the folder, too. This will rename the catalog and all the files it uses for proper operation and put them in folder with a name containing Version 14.. You are then left with the older catalog files and associated files that will not have Version 14 in the name. Thiis process also creates a folder with named somthing like "Old Catalog". In that folder you can find all the old files. At the least, delete the file containing the words "Catalog Preview.lrdata". You should see that folder is extremely large and deleting it will provide the fastest way to recover disk space. Then... empty the trash.