To change field type for custom field in web, please follow below mentioned steps:
Step 1: Click on Document Setting on sales dashboard.
Step 2: Click on Add Custom Field.
Step 3: Select the Custom field and click on Edit.
Step 4: Check the type which you have selected.
Note:
1. In Number field mention only numbers.
2. In Text field mention only letters.
3. To enter Text and Number both please choose field type as Text Area.