how to delete some of the data in the time capsule

No, it is nearly impossible to mess with the TM backup. If you do the chances of having usable backups is minimal. You can try limiting the size of the sparsebundle.. but you cannot go backwards.

I am not sure what you are trying to achieve.. perhaps spell that out.. but if your TC disk is full, my recommendation is to archive the existing backups to USB drive plugged into the TC.. this is available via the airport utility disk tab..

Then erase the TC.. also on the disk tab.

And start new backups for all your computer/s.

Once you have a few months worth of backups the usb drive can be erased as the chances of needing an old file is very unlikely. Up to you though.. you can keep it forever if you want.. or at least until the drive dies.