So, you have some different decisions of your case.
1) If you have KX-T7633/T7636 Digital Proprietary Telephone connected to your KX-TDA200, you can purchase an KX-T7601 USB-module, then install this module into your KX-T7633/7636 DPT, connect your PC to your DPT by USB and then program your KX-TDA200 system via digital port of your DPT.
2) You can buy KX-TDA0196 Modem module, install it onto the MPR-card of your KX-TDA200, and then program your PBX via telephone line by using modem and calling a virtual number of this Modem card at your PBX.
3) You can buy KX-TDA0410 card, install it into your KX-TDA200 system and then program your PBX via LAN.
4) You can upgrade KX-TDA200 to KX-TDE200 by replacing current MPR-card of your KX-TDA200 with an IPCMPR-card for KX-TDE100/200 systems (KX-TDE0101). New IPCMPR will give you:
a) Remote programming via LAN (like KX-TDA0410, but you don't need a free slot in your PBX)
b) CTI applications (e.g. Panasonic Communication Assistant) usage, and you still don't need KX-TDA0410 and free slot
c) Two voice channels for SVM (Simplified VoiceMail) and DISA/OGM features (you don't need to use KX-TDA0190 card and KX-TDA0191/0192 module)
d) Ability to connect SIP-trunks and SIP-extensions (not supported by KX-TDA200), H.323-trunks to interconnect with another KX-TDA/KX-TDE system (KX-TDA needs an IP-GW4/IP-GW16 physical card and a free slot to it) and IP-Proprietary KX-NT-series Telephones (TDA needs IP-EXT card and a free slot to it). BUT!!! If you want to use those abilities, you should also buy a DSP16 or DSP64 module, install it onto new IPCMPR-card, and buy and install appropriate Activation Keys for your new KX-TDE system.
5) Another way is to upgrade your KX-TDA200 system to pure IP-system KX-NS1000. You need to buy KX-NS1000, DSP-card to it (DSP-M, DSP-L or DSP-XL), Stack-Master card (KX-NS0130) into NS1000 and Stack-Slave card (KX-NS0132) into your KX-TDA200 (instead of current MPR-card). In that case you'll have a powerful IP-PBX with your old KX-TDA200 system as a gateway for non-IP trunks and extensions. Of course, as an IP-PBX, KX-NS1000 can be remotely programmed via LAN or Internet.