Replace electric heater
You will have to find out the electric heater KW is. The direct replacement is the best. Usually, there is a label on the electric heater that will tell you heat strip part number. If there is none, the general rules are:
1.5 Ton to 2.5 Ton = 5, 8, 10 KW heat kit
3 Ton to 3.5 Ton = 10, 15 KW heat kit
4 Ton = 15 KW heat kit (some will have 20 KW, rare unless you live in a region that has rigid winter)
5 Ton = 20 KW heat kit
Please consult your system manual or installation invoice.